I like to use the settler to rebuild Valencia 1S. The AI seems to like to found Girona 2E of Barcelona.
Capturing Palermo is definitely possible, but it is harder than one might expect. Certainly one of the harder UHV's. Basically you have to build ~2 trebuchets in Zaragoza first thing (trade techs with the pope), cogs in Barcelona and as many Almogavars as you can.
The AI does indeed settle on the salt east of Barcelona. I take the second settler to the marble (although I hate settling on resources

) north east of Barcelona and settle
Perpignan (oddly, in Provence). Not that you particularly need the marble as Aragon, but it gives a foothold in Provence which I use(d)as a base later to take over Provence in its entirety for the third UHV, which means conquering Marseille and Cannes, considering the AI's new fondness for settling there (it seems to like salt!

)
I would also concur with reworking the first German UHV as it is rather easy and trivial. In RFCE it involves conquering two independent cities (Lübeck and Milan) and settling the rest. On ocassion it requires attacking a Burgundian settlement in western Swabia (Fribourg normally).
Actually I put that as the UHV because it is the capital of Norway. The North Sea Empire contained all of Norway but I though that would be too difficult to do in time in case you got a powerful Norway.
Indeed, and understood, was just that I wanted to enact the Danish-Norwegian union and relates more to a personal distaste for conquering capitals and potentially collapsing civs. I hate huge swathes of independent cities. I've seen Germany, France and Poland collapse leaving the whole of Western and Central Europe independent.
Perhaps. Did you manage to win the current UHV yet? Was it not quite similar to this? Or did you have to do something silly like taking a boat to Spain?
As indicated in the screenshot above, Spain collapsed

I haven't played that far yet but will give feedback as soon as I can.
Aragon UHV
In the first instance, AI Spain really doesn't seem to make an effort at getting rid of Cordoba, and neither does Portugal. Cordoba still controlled most of the Iberian peninsula when Aragon arrived, including Toledo and Barcelona. Sometimes they even control Bordeaux or Toulouse! (In the shot above from the Sweden game, Spain collapsed and Cordoba is still firmly in charge of most of the Iberian Peninsula).
It took me about 60 years to do Spain's job and clean up the Iberian Peninsula. I had to hire all the mercenaries to prevent Cordoba from doing exactly that (and it does often), but mainly used the initial Almoghavars (sp??) and, if you're lucky enough to not have an Andalusian Duchy to the south (i.e. a Catholic Cordoba), the Pope's (rather small defensive crusader force of) two armored lancers and two macemen.
I camped the mercenaries just outside Valencia and Cordoba sends the bulk of its units there (rather silly, but anyway). I started cleansing Spain by taking back Toledo, Cordoba and two other cities in the south and gifting them to Spain as I go along, healing my units in those cities before I move on.
I took back Valencia finally, had Cordoba capitulate and collapse a few turns later anyway. In the mean time I trained two cogs in Valencia and took the initial four almoghavars, the two macemen and two armored lancers (one of which was a mercenary unit with the amphibious promotion) to Palermo in a rather arduous back and forth journey. I upgraded the lancers to knights first, and then took the one with the amphibious promotion first to clear a landing spot and I slowly landed the eight units in Sicily south of Palermo. Capturing the city itself wasn't too difficult using the right units against the Sicilian units. The transporting and landing is the tedious part IMO.
I then took two Almoghavars to Naples (who only had two archers and no walls), and took that easily.
In the mean time Valencia and Barcelona were spamming ships (mainly war galleys - later upgraded to Gun Galleys - and two extra cogs for the transport to Sardinia, Corsica and later Thessaly). I find the war ships useful for protecting coastal resources and station them around the Belearic Islands and Iberian and French Mediterranean coasts.
I settled the two Great Generals I got in Zaragoza (one which irritatingly spawned in Palma de Mallorca!) and built the Heroic Epic (the marble from Perpignan did actually come in handy!). I then created about 8 - 10 Almoghavars and stationed them east of Perpignan on the border with Burgundy (when the plague came, it killed three ships (weird for a plague!) but fortunately the Almoghavars were safe despite plague all over Provence).
I used my cogs to inspect Sardinia and Corsica (settled by Genoa of course) and started the invasion of the Islands from the base in Palermo, taking the "amphibious" knight to directly land and assault the swordsman Simone stationed in the one Sardinian city.
I took all the military units from Palermo (with the exception of the Pope's two knights) and stationed them in the city on the northern tip of Sardinia, the southern one was still Genoan. I left the two macemen in Sardinia and landed two knights and four Almoghavars just south of Aiaccio. I easily took the city, healed and moved back to the city in Sardinia, and landing my troops one tile north west of the southern Genoan city on Sardinia. Taking the city was easy too, and Genoa signed a peace treaty, and a few turns later wanted to be my vassal.
Burgundy asked that I protect her too, but I declined and declared war instead, invading a post-plague Marseille and Cannes swiftly with four / five Almoghavars each.
I even had time to settle Syracuse, the city on the southern most tip of Calabria (the province south of Apulia) and La Valetta on Malta (was the latter not previously a requirement for UHV-3?)
The 25 ships was easy as I made most coastal cities produce at least one, while Valencia and Barcelona created the bulk of the ships. After I met UHV-2 I took my original force against Cordoba (the four Almoghavars, the two knights and macemen) just west of Athens after declaring war on Byzantium and took that city easily as well.
That was it really. I have to say that I think a lot of the military success will depend on a handful of units in top form and carefully tended to and promoted. Maybe that's why it is actually good that you have to take out Cordoba first.
Aragon-Castille Union
I saved prior to winning third UHV and gifted Athens back to the Byzantium on reload to see what an Aragon-Castille union (with the former dominant) would look like in 1488. This happens after an Aragon Historical Victory so I personally don't see the use of such a union for either a human or AI player (the latter for historical reasons).
Spain, not having waged as much war on Cordoba, was a formidable opponent tech and score wise, pushing out wonders too. I ensured I had enough money to buy the Union (I find that often makes a huge difference) and succeeded.
I got all the Spanish possessions (with the exception of Jerusalem and Tuscany, which they seem to conquer now too), but it was a huge unstable empire. I played until after 1500 and my stability was unstable at -16 / -18. (I didn't bother with the Imperialism civic before the Union and didn't adopt it afterward either because stability was already bad).
Genoa took control of a crusade, declared war on my other vassal (Byzantium) after renouncing my protection, and then conquered Constantinople. I conquered Genoa and Milan (gifting to France and Germany respectively), and recaptured Constantinople. I couldn't gift it to my vassal Byzantium, so stability dropped and I was collapsing.
I quit the game seeing no further purpose in playing Aragon having successfully (if one can call it that) united Spain under the Crown of Aragon. So the Union with Aragon is possible, but probably unfortunate, both practically (for game and stability purposes) and historically.
Concluding thoughts on Aragon
I think the conquest and control UHVs are interesting and challenging, because they require some careful micro-management, if you will, of a rather limited military force initially, which can be successfully transformed into a highly skilled one.
The 25 ships is a bit boring, but not impossible and not entirely useless
I didn't use their UB that much, building it for the sake of it, but still using two cargo capacity cogs
en masse.

Their UU is definitely an awesome addition

(except against macemen with their +25% against polearms, I think... but their great for cavalry and early ranged units, especially with the city attack promotions).
All-in-all I think Aragon is a great addition, both for the player and the game in general (as AI), and the potential (and quite frequent, if not normal) absorption of the Crown of Aragon into the Kingdom of Spain led by Castille is a good thing too, historically anyway.
It seems unfortunate that you have to conquer Marseille and Cannes, when Aragon historically only controlled what is the in-game city of Perpignan, but it makes it challenging (and Burgundy gets absorbed into France anyway).
I would kinda agree with AdrienIer on the army size, especially if Cordoba is Catholic and there is no defensive crusade. Cordoba has become an apparently formidable entity on the Peninsula. But I still think it is possible to outsmart it with effective micro-management of troops.
EDIT: I find it funny that Swedish naval units also get the promotion against cavalry, it's not a major issue, but can it be coded to be for land units only? It's mainly for cosmetic reasons and tying up odds and ends, but just a thought
