I did preplay with the arabs and the Byzantines.
(preplay Arabia)
I used the arab exploit Absinthered recommended (when it was still possible) to get judaism (and islam and orthodoxy and catholiscism) early on.
Summoning hordes of spearmen (by razing preplaced towns) hurt Byzantium surprisingly little.
(they pillage some improvements but are below the treshold to capture a city so they make the defenders a little tougher, giving them better chances against the tough barbs that autospawn)
The barbs that flipped to Bulgaria actually appeared to harm them because they suicided them along with their koniks against Byzantium and the barbs early on (once again making Byz stronger)
(Byz Preplay)
Razed most of the byz cities on flip back and built Marco Polo (the wonder helps a lot)
Razed independent cities in areas stable for Venice.
Arabia became very weak very soon without the Byz cities to buffer them from the barb attacks.
(this is definitively the easiest way to get 2 out of 3 UHV's for Venice very soon. It has the added benefit that you will get declared war upon by Cordoba and Arabia, two arabic civs comfortably far away that when at peace tend to snatch away your desired wonders. Oddly enough the bonus to military production is almost negligable because of the crusaders you receive supply enough and better defenders than you can build yourself.)
Venice
The first two UHV's vor Venice were fun and easier than they appeared.
It pretty much tells you where to build most of your cities (with your initial settlers) and the conquest of even a strong Byz is surprisingly easy. Around the time you built your stack of cata's they are under attack of some rather nasty barbs. Giving you ample time to bombard and SOD whatever force they have in their capitol. (You definitely need no preplay for this part.)
At about 2/3 of the game I experience a big drop in stability. Making the strategy with lots of religions and as few cities as possible unfeasable for me. (this drop also happened when I was almost entirely monorelious)
The final part of the UHV is the tricky one.
I discarded my first attempt after I found out that the civs with the atlantic acces (AA) actually need to build the workboats for the atlantic acces resources to be tradeable (if they are tradeable at all).
Hungary was a pest, I had a lot of wars with them.
In my second attempt I captured a collapsed Lisboa to secure the AA myself. When I ferried my armies back to My main cities to fight off the anticipated Hungarian attack I was backstabbed by Spain.
In my third attempt I kept a big army in a fleet halfway between my core and Lisboa. Oddly enough this time neither Hungary nor Spain declared war and it was smooth sailing towards victory.
France was very strong in this game. It gave me a lot of worries because they stayed on par with tech and had about twice my production. Bibliotheca Corvenna was a godsent to put some techspace between us. On the other hand they provided a nice target to steal techs from.
A little luck may be involved as in one game they (the French) went straight for the colonies and in another they opted to go the military tradition route.
Turkey sometimes is a nuisance and sometimes just gets pwned by the barbs.
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offtopic spoiler)