Heney, I certainly do wish you luck and your plan sounds great to me. Those charges seem a little stiff but I'm not familiar with RCCL's vow renewal package.
Back in Feb. we went on a 10 day Princess cruise ( Coral Princess ) and I surprised my wife with the wedding vow renewal. It cost $ 200.00. We got a bottle of champagne in the cabin, a bouquet of flowers for her, a lapel flower for me and complimentary champagne at the lounge where we were waiting for the ceremony. The ceremony was private and performed by the Captain in the small chapel. We got a free 8x10 photo of our choice framed in a beautiful silver frame. Although there were 2 other couples who were doing the renewals, all three of us were given a private ceremony by the Captain.
I don't know if the renewal thing had anything to do with it or not but a few days later we recieved an invitation to tour the bridge of the ship. There were 9 couples on the bridge tour and of the 9, 3 were those of us who had done the renewal. Maybe we just lucked into something but for what we got for $ 200.00 was, in my opinion, a real bargain.
I can't remember for sure but it seems like I booked the package only about 2-3 weeks prior to sailing .
Anyway, doing it your way sounds like a great way to go. Good luck and enjoy.