Good questions! I'm no expert, but I'll give 'er a shot.
#1 Nothing you're going to buy will have a fully
supported chamber. That said, Glock took full advantage of the bottleneck cartridge and the chambers are more supported than any of the other calibers chambers. If anything, if you've got another barrel already in the budget... I'd buy a stock G32 barrel for some added velocity.
#2 I use the stock barrel. Only reason I would see the need for an after market barrel would be for shooting lead. As long as you're sticking with jacketed/plated bullets the stock barrel is more than fine.
#3 I've never had experience with Redding, I've heard nothing but good things about Redding though. I'm using Hornady's CGND Ti Nitride dies and the Lee Factory Crimp die. This set up works great for me.
#4 This is one I'm leaving to more experianced. Check out Pete's page for a bunch of good reloading info. HERE
Any other questions you have for reloading I would pose in the reloading subforum here on gt. The guys in there know about just about everything under the sun, and if they don't they know right where to point you.
#5 Can't speak on this either. I got set up to reload the 357 sig the same time I got the handgun. All my practice ammo is reloads.