1. Depends on each individual manufacturer. Why not try a small Borg Warner or Bullseye turbo? We have had GREAT luck with them. S256 or slightly smaller would be a good choice if you are looking to do this on pump gas. The extended tip turbos spool VERY quickly. Billet wheels seem to be the new big thing. Not sure how much faster they really spool as it seems to spool similar just make a bit more power. Usually they are a slightly larger wheel.

2. Later spool sometimes, but higher hp

3. The is a ratio between the inducer and exducer.

Honestly if you have the bottom end to handle it, go bigger. Lag is only there for a second in first gear. From there, it's just a downshift away. And put a filter on that thing. You are just sand blasting your compressor wheel!