if you want a 33X12.5 and want to run it on a 16" rim...then just buy a 33X12.5R16 instead of a 33.X12.5R15. Companies tend to make the really popular tire sizes (33X12.5, 35X12.5, 37's) in a variety of rim sizes (15's, 16's, 17's, 18'2, 20's)
As far as rim choice goes, if you have a source for the Moab rims at a good price and you like them, then just get them. Just don't pay full pop from the dealer. If you wheel reasonably hard, you're going to get rock rash. That is unavoidable, and is true if any set of rims you buy. Rocky mountain pinstriping and roch rash on your wheels is part of wheeling.
Running a set of 1.5" inch spacers will work just fine....if you own a torque wrench and know how to use it. If you don't know how to use a torque wrench or are not willing to spend the time, then don't get wheel spacers. A number of oflks here (myself included) have run good quality (hub centric machines aluminum) wheel spacers for quite a while and have had no issues. Yes, wheel spacers will shorten the life of your unit bearings, but so will running wheels with lower backspacing. Running proper wheel spacers will not hurt your wheels...just don't buy the shim type - make sure you get the style that has a set of lugs in them.