Yes, a new mesh for each emitter. This is a good idea in my opinion as if an emitter is behind the camera the particle mesh won't be rendererd, however, if all your particles are in the same mesh all the particles will be rendered regardless of if they are in view or not.
With all cases? Someone posted that if you make 2 vertices of a tri the same, that tri won't be rendered at all. I use this now in my current quad system and it does seem to be the case.
That's pretty straight forward, a UV co-ord goes from 0-1 so if your texture is 512x512 512=1 and 0=0 so .5=256, .25=128 etc etc, very simple.
Yeah thanks, I wasn't thinking.
Again it's a balancing act (varying from card to card), personally I'd stick to quads as it make UV mapping a hell of a lot easier. Unless you're talking about 100,000s of particles I don't think on modern cards your really going to make that much difference. Triangle count isn't really the problem here.
I'm using both quads and tris. I already have the UVs all setup on the tris, they do allow the fps to stay a little higher...