I am not good at the math and figuring which is the better value, but I can answer these two. You would have to do a split stay and you would not be guaranteed the same room, although they do try to keep you in one room they will not guarantee it.
keep in mind if you do any of the signature dining ( Hoop Dee Doo, CRT, Spirit of Aloha) the gratuity is included. so you may be using 2 credits for those, but you do NOT have to plan for additional tip.
