We have 3 people newly joining green so I'd go for that if you wanna play with Bay people. But I answered your question in some detail below.
So how are the factions different gameplay-wise?
Thunderstorm got busy with his porn business and then tried to make warfacts 2 instead of adding to one which didn't go well. So faction differences are not actually implemented. There are 3 valid empire types, which are faction agnostic that work.
Corp has lots of player banks, gives some small interest per game tick, confed lets you share fleets, religious gets bonus pop growth from age of empire and number of worshippers. I run a religious one, pop growth starts early compared to interest and its more useful until people are super rich.
Your faction just defines where in the universe you start and who is on your team.
The game is currently maintained by a volunteer web dev who doesn't play anymore, so new features don't happen. Most changes involve altering the round set up every round, faction numbers, lost, landmass growth, starting tech and such.
I once tried to implement my own version but I ended up moving on to 3DRTS instead. Someday someone with knowledge of web dev and free time might upgrade features.