1) Relative sync currently only works on Record operation, not multiply, etc. Since multiply is kind of special anyway (in terms of it always making the loop longer/shorter by a cycle length, you can get what you want (I think) by actually turning off quantize.
2) Hmm, so pitch (and i assume stretch) aren't working for you at all? Strange. Anyone else seeing this around here (as if they are reading this
3) routing audio from one loop to another would have to be done in the host, SL doesn't do anything internally for you there. Yes, as you've probably discovered you can route separate outputs too. I hear you with regard to mono, etc. I was just running into some weird stuff trying to support different plugin configurations back when i first implemented it as an AU.
Yes, go ahead and increase the loop time minimum as much as you feel is necessary, it just uses more RAM.