My 18yo daughter, who has celiac disease, just came to Vegas with us and we found a few good places. Maggiano's at the Fashion Show Mall right across from Wynn has a GF menu. The chef came out to us which is always comforting to know that they "get it." Any of the better steak houses will accomodate. PF Chang has a GF menu and several locations. For breakfast, The Cracked Egg was OUTSTANDING. You will need a car to get there, though. Check out the web site for locations: https://www.thecrackedegg.com/.
Sounds like you are new to this so I might respectfully comment on navigating around buffets. They are a cross contamination nightmare both out on the floor and out back during prep. I would be really careful. Additionally, they have no reason to worry about GF food so many things have hidden gluten in them. For instance, we inquired about the omlette mix at one of the buffets, and modified food starch (gluten) was in the omlette mix.