You've got the right parts. If the belt skips a little, not a huge deal. If you want, you can tighten the pulleys up a bit but that will be a balancing act between belt too tight with too much drag in the drive line (inherent to belt drive) but not skipping and belt just right how you have it now and skipping. Just gotta play with it. I think the exo locker hub or the center diff is the way to go, but there's give and take to everything.

Don't need overdrive with the exo locker or center diff.

+3mm wheels are a must have.