We've considered something similar and while I can't comment on the resorts themselves, I wanted to make sure you were aware that FS has 4th night and 6th/7th night free offers starting September 1. (I believe that is the start of rainy season....so also check your weather). A FS preferred provider will also get you free breakfast and the possibility of an upgrade.

Oh, and I think Praslin and La Digue are close together so that you can do both in one day trip.