I've partially played through two different games now and had a different blast on each one of them.
First up was an Immortal game as Boudicca. I just read your Wide guide yesterday which used the Celts, so I decided to just play copy everything you said there.

Adapting a bit for the mod, of course... I was in a T-shaped continent with Polynesia and The Maya. Pretty funnily, even though I forward settled Polynesia with my second city, they took a huge while to start hating on me. Even as I made a total of 7 cities, he just never got around DoWing me... Kamehameha and Pacal were too busy trying to murder each other, I guess.
I eventually joined the war against Polynesia and took a single city, while Pacal is still best friends with me to this day. Though he wiped out Polynesia, so I'm SURE he's coming for me next... >_> Too bad Rome was in a nearby continent (connect by coast!) and decided to storm one of my coastal cities first.

Even though I had nearly 10 gattling guns, they were no match to Cesar's infinite Galleass's. He even came with some Ironclads later. That city is still mine, but not for long. And I'm not sure I can hold him back from invading my continent. >_>; Are these naval attacks a new feature in v4? I never had those happen before. Though this game IS quite atypical, with Cesar alone in a separate continent which connects to mine via coasts. So he had plenty of space to cityspam and build a navy of death. Things look grim, but maybe I can defend myself and still win this.
That was quite depressing, though, so I decided to start a completely different game to freshen things up.

I went the totally opposite way, still on Immortal, and picked Venice to see how long I'd last on a single city. And the answer was... not too long, heh. I had China and Carthage on my continent and they both opened Honor. I managed to bribe them into killing each other (guess I wasn't that nice of a target or threat with only one city and all) and their war was... quite stale, really. A central city kept flipping owners and that was it. Eventually, I decided to build some Great Galleasses and join the fray by taking some of Carthage's coastal cities. That went nicely! Way too nicely in fact. After I took those two cities, Wu Zetian managed to completely wipe Dido out of the face of the planet... And came after me. Guess my capital doesn't have much of a chance against her 10+ cities.

Still, it was a fun game. Just teaches me that I should let people murder each other rather than helping one side.
I'm trying another game as Venice now, but I also think it won't work very nicely. As you can see, I'm not a very good Immortal player.

But it's nice to see how long I can last before everything goes down the drain. And I still have some chance in my Celts game, so there's that!