Hi Sarah, and welcome!
I would finish the walls first, with the exception of the floor moulding. You'll want the tile grout to cure, and you'll want the sealant for the grout to soak in and dry without all the drywall dust you'll be creating. Go ahead and paint before you lay the tiles too, and when the tiles are finished all you'll have to do is put in the trim.
Good luck, have fun, and share some pics!