I think that several of these things have already been decided on by Gavin.

I don't know exactly what he has done, but i'm sure I read somewhere that if say, the Anticans join you, then you will never get the Selay to also join you.

The game is gonna be far more 'intelligent' than its predecessor, and both long and short-term trends in attitude change will be worked out properly by the game. The races will act accordingly, rahter than randomly declaring war as they used to.

The addition of being able to send messages and receive replies also means it will seem far more realistic.

There shouldn't be any need to worry, Gavin has thought of these things, so i'm sure you'll be pleased with the results.