I'm one! It's better to start with someone who's already chubby for sure, firstly because I just tend not to find muscular or skinny guys attractive at all and therefore would find it hard to muster enough interest to feed them, and secondly because it's nice to be able to see a feedee's potential...

I think both slow and fast gains have their merits. Drawing things out gives you a really interesting, hot progression, and makes you really anticipate each little expansion of the body; trying to gain quickly means you stuff your feedee more, can tease them about their growth, or punish them for not gaining enough etc. Trying to gain quickly is hotter in the short term, but not very sustainable.. I would probably go for slow gain as a background thing, and have periods of fast gain when both of you are feeling up to it.

2 or 5! The two are quite different I know