When I replaced all my stuff, I didn't replace the thermostat housing, just cleaned it up in our parts washer at work. It kept wanting to leak though around where the upper radiator hose was attached to the thermostat. I didn't have one of the constant tension or spring style hose clamps and just kept tightening it and eventually it stopped.
IMO the belt and everything on the front is one of the easiest engines you'll ever work on. Go ahead and replace your belt and keep your old one as a spare if you want, because you can swap that in a few minutes in the field.
Which style of fan do you have? My Wrangler has the type that with I believe it's a 1/2" wrench and sturdy screwdriver you can have on and off in just a few minutes. If it's the style like my Grand Cherokee has, then I suggest borrowing/getting the special tools from an auto parts store. Though the tools aren't necessary, I'm not good enough to do it without the tool.
If your this involved, take a look at your harmonic balancer. Look for any dry rot or anything that looks like it isn't new. Check your pulleys as well and replace any that act suspect. Heck you can change your timing chain in like a half hour or so once your harmonic balancer is removed.
