To answer your questions in order: Yes. Yes. Yes.
Hence why I'm fairly jealous of Kai conquering carlwolcott's planets, they have ridiculous population levels for their society level because he seems to only log in once a week 
Trust me there is no difference between 1000 and 20000. !@#$, I make 28 steel a turn. Damn. Home planets are the only important ones.
Personally, I'd rather see planets be useful sooner so that I can expand quicker and have a safety net in case someone attacks me. But if you plan on spending a lot of time away from the game or not being overly aggressive right now, then slower population maxing is fine.
Wrong, !@#$ty colonies makes being aggressive the best thing to do, to capture home planets.
