Guess I am feeling a bit more ambitions today, especially since keycocker was kind enough help out some...
Big Fish Little Fish has the cheapest snorkel rental, if you are not taking a tour. $2.50 US per set / day.
Keycocker commented on Seaview not Seaside Cabanas, and I believe your question was about Seaside Cabanas -
Seaside cabanas is one of the newer upscale accommodations on the island. You chose well.
Next time you may also want to consider "Diane's BEACH House" for you and your family: Two Bedrooms, full kitchen, living room etc. www.staycayecaulker.com/beachhouse.html
About a private beach - it wouldn't be private anymore if we announced it here! Good luck finding your spot!