Better spring for a sturdy belt, too. A 4" GP100 is no lightweight and will quickly bring lesser belts to their knees, and have you feel like you've been tourniquetted at the waist. I know. I've tried.
Solid belt, leather. Minimum 1.25" and double layered. Wider if you can find it (and if your belt loops will accomodate.)
Also, start saving up because at some point you will begin considering something else for everyday carry. I lurvs me some GP100 but they are just too bulky and heavy for a practical all-around everyday carry piece. Even my 3" SP101 is burdensome after a few hours. If you want to stick with .357, seriously consider an LCR or a S&W Airweight. You lose one round bu the trade off in weight and bulk is ever so worth it.
I'm serious... keep the GP for OC/home defense/range, but seriously consider getting something more practical in terms of size, shape, profile, and weight for everyday CHL duty. I tried carrying a GP100 (and an SP101, and a 1911, and a Glock, and an XD9) and I eventually found myself making excuses to not carry on an alarmingly regular basis. When I finally backed off and took a more objective approach I ended up with a much more satisfactory result.
Brad