Don't be sorry! That's what a forum's about.
1. I'd say around 20.
2. I'm not using an air floor, but I'm planning to build one. Since I grow in a gro-tent instead of something I built, I'm going to have to get creative, but I have a design in mind to replicate the effects of the air floor. Basically gonna make a sealed riser for the floor, run the air intake into it and drill some holes.
3. I actually always use 2 plants per bucket because I have a very small veg area, but yeah, around 16-20" per plant from the v where you topped.
4. Because I use 2 smaller plants, they train around the bucket in about 10 minutes. Doing this kind of training with a larger plant with a woodier stem takes much longer (done it a couple times), so to me that's one more pro for using 2 smaller plants per bucket. I space the holes about 4" apart.
Thanks for checking out my grow, ask away and I'll do the same.