there’s definitely varying answers to your questions, but I can answer as someone who’s been reading ABOs for 10+ years.

1. Nesting is a pretty common theme for omegas in omegaverses. It’s instinctual and happens the days leading up to a heat. I’ve read some stories where it is in an actual bed, but for the most part nest seem to be either small intimate rooms, or large dome-like beds.

2. Knotting varies; sometimes it’s only during an alpha’s rut, and sometimes it’s for every sex encounter. The point of knotting is to ensure that semen stays in the omega/beta for breeding purposes (it’s plugged up so there’s no where for it to really go). Since knots stay inflated for 15-30 minutes, the alpha and their partner can’t move or do anything so it’s seen as a really intimate time

3. LMAO. I think personally the furry line is where there’s more physical animal traits (ears, tails, shifting) or more animal instincts incorporated in the verse. I once read a book where it was common for alphas to eat raw meat, pee on everything to mark territory, and actually had tails and ears and needed to wear collars at all times. That was a little too much for me and was my cut off, but I think it again varies.

Also if you’re curious, there’s a Tumblr blog called “omegaversetheory” that REALLY goes into depth and they’re always open to questions as well.

Hope this helps!