Pivot size is totally up to you. I started with 3/16 pivots with 1/8th stop pins, but I have also used 3/16 stop pins.
I buy inexpensive reamers on eBay and at the speed I make knives, they last a long time. (I'm slow)
I've recently started tooling up for 1/4" as well but only because I had someone request 1/4". I really like the versatility of 3/16". Most of the pivots and stop pins I've bought have been from AKS.
Also, I'm very new to folding knives so hopefully there will be much more experienced guys come along, I'm just passing on what works for me.
Good luck and keep us updated with your progress!