Unlike oils, acrylics can be used directly on paper or fabric without priming. The difference is one of handling, not of any sort of permanence. Unprimed surfaces are more absorbent, so some sorts of applications will be easier, some harder. Acrylic gesso is the standard priming for both fabric and paper.
Yeah, I painted on a lower gsm BB with acrylics once before and it buckled badly so I'm probably a bit wary now. I also didn't like how the paint took to the surface so the absorbancy thing might have been the culprit there.
Sounds like some experimenting is probably in order after all. No point starting in on a major project and finding out halfway through that I don't like the surface or having it warp on me.
Thanks again for the input, it's much appreciated.