Depends how much room you have. If it's only a small home studio setup 100mm will be too long. Nothing wrong with a 50mm. Nice lens for not a lot of money.
I agree.
I have gradually gone away from zooms, and although I still have a 24-70 and 80-200, I use primes wherever I can, and in the studio I Always use primes.
In a studio environment, where you can move around, a zoom is less important.
Primes are sharper, faster (although with studio lighting you won't need the extra speed, unless you want the shallow dof), and much lighter.
As for focal length on a crop, either the 50mm AF-S or the 35mm AF-S lenses are super sharp for next to no money. They also have a good, natural looking apparent perspective, which is flattering. Sometimes with a zoom like the 17-55, if you are too close, and shooting at the wider end, the results can be very un-flattering. This happens less with a 35 or 50mm, as you would need to move back, instead of zooming out wider with a zoom.
In my opinion a zoom is a little more convenient on location, where "zooming with your feet" is not always an option, although I personally would still try and use a prime whenever possible.
Good luck with your decision, and let us know your decision and let's see some shots !!