Society only goes up if you're active, right? It stops if you go inactive?
But... does population growth stop if you go inactive?
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
I got some half decent planets when I got PeterKaan's planets, but he'd only been inactive for a few days so they weren't that inflated.
Growth depends on the society level though. So if you leave a level 10 planet for 5 days, it might not be as good as a level 11 planet left for 4 days. There's also the problem of people noticing you go offline and seizing on it.
What you do depends on how long term you want to play the game. "Eventually" planets will max out no matter how many arcs you send, or time-outs you have. Planets start to lose population when they hit high 80s, but only if you're at max population (just try building loads of fleets and watch your population increase again next turn). So if you send 5 arcs to a planet, you might hit your limit at level 100 instead of level 120 if you sent 1 arc (guesses on numbers, btw).
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.
