I ride Moab a few times a year, preferably January through May before the tourists and the heat, February and March are my favorite months to be there. If I am riding there from June through September, I’m on the trails early, like 0400 early or I’m doing a night ride, riding in over 100° heat during the day in Moab can be dangerous, you will be exposed. It’s best to ride on Wednesday and Thursday to have the best chance at the trails not being over crowded. To truly experience Moab mountain biking, you would need several days, but you can definitely get a good taste with a few days of riding.
The Klondike Bluffs trails are great to get started and a fair representation of the beginner to intermediate trails throughout Moab.
Slick Rock trail is iconic but busy and very exposed, usually a good 10° warmer than forecast due to the landscape. I generally only ride it when someone in the group hasn’t and really wants to.
Horsethief and Navajo Rocks are also great trail networks for an intermediate rider.
The Whole Enchilada route is well worth the cost of entry, but you’ll need to now your limits and commit to the trails. It can be brutal.
If your coming up from Vegas, I’d recommend spending a day in St. George or Hurricane and riding Gooseberry Mesa, by far one of the most picturesque trail networks in southern Utah.
The two most important pieces of advice I can give are to have extra water and run tubeless with a couple extra tubes. Walking out with a flat while being dehydrated sucks.