Hello and welcome to the RTA forums !

Your trip looks reasonable and relaxed, although I would use 'that day in Vegas' to stop a little longer at the GC. Williams or Flagstaff would make it an easier drive and offer better value lodging on arrival. You could go from either town and head North on US89 towards Cameron and come in the East entrance along Desert view drive [64] near Cameron and then into the village area for perhaps a second night. Visit 'Hermits rest' on the free Shuttle bus and leave by the South kiosk to Vegas and you have completed a nice loop of the South rim. It would also leave you a little spare time to drive part of old route66 through Seligman and perhaps stop at the Hoover dam.

Tijuana is recommended as a 'no go zone' what with the drug cartel wars going on, it isn't worth the risk IMO.