Ohh, I think this would be a really fun room! For the sarcophagus, I would start with a wood and chicken wire frame and build up with paper mache to look like whatever sarcophagus guy you wanted. You could even inset plastic jewels from the craft store for scarab beetles, etc. Then spray out in gold and add heavy distressing and washed out color detailing.
Trim work for the room would be easy I would think. Just google egyptian tombs and get some inspiration. Some columns maybe with faux fire torches, etc.
My mind immediately went to the movie Stargate and the portal as a possible gateway. That might be a good movie to visit or revisit for some creative inspiration.
I LOVE mummies and all that good stuff and would love to do a room like that!!!!! So many ideas already....statuettes of cats and urns for the removed body parts....so cool!!!! Good luck to you!!!!