There are other threads about this same topic, but here's my take:
1) Harnesses. And, if you're not rolling with aftermarket seats with pass-throughs, get the DragonFire racing bezels or the strap stays to keep the harness straps from sliding apart around the stock seats.
2) Full UHMW skids with trailing arm protection and rock sliders. And, if you don't have high clearance A ARMs, get the A ARM protection, too.
3) Larger tires. There are those whose opinion is that for a 4 seater rock crawler 32 inch tires are the minimum. Make sure to have a nice plug kit with air, too.
4) Clutch Kit. If you're running larger tires and running aggressive rock crawling lines, you'll want a clutch kit. Lot's of options are out there for a XP4 1000.
5) Winch. Not as critical. But, given the XP4's increased likelihood of getting high centered, I'm a huge fan of winches. I've used one on each Moab outing to either get myself or someone else out of a jam.
6) Take a few machines. Having more to enjoy the beauty in Moab is more fun. Plus, having more muscle or go-get-help/supply vehicles is priceless if you need them.
7) Maps or GPS. I use a 7 inch Samsung tablet and Backcountry Navigator Pro. Even though the trails are decently marked, it's just a smart idea to know where you are and how to get out, especially in an emergency. PM me your email address and I can send you a KMZ file of most of the major trails.
There is a ton of other things to consider, too. But, that's my list of must-haves. Have fun!