The type of gun (gravity/siphon etc) should be determined by what you want to spray. Some turbines allow you to run a small pressure pot which in turn allows you to have a much smaller, lighter gun in your hand which increases your flexibility.
As for sanding between finishes, you really aren't "sanding", just scuffing. You only "sand" if you are trying to level out a surface, eg after multiple coats of sanding sealer or grain filler. Personally, I scuff between every coat, regardless of the type of finish I am using. It's just sound practice and IMO gives the best results.
I really don't have any recommendations for brand as I have no experience with a sufficient variety to offer a meaningful comparison. I have only ever used one turbine system in my life, it's at least 20yrs old and now sprays stains, dyes, toners and washcoats.
Finally, I would encourage you to go to the folks that sell these things and pick one up, preferably full of liquid, to see if the gun feels comfortable to your wrist/hand.