We are thinking of sailing ourselves or, more probable, hiring a delivery captain to get our boat to St. Thomas. Are there seasonal slips/moorings say between late Dec. and April? If CYOA had availability that might be perfect. Any suggestions appreciated.

Unlikely to find a mooring for seasonal rental that time of year - but a possibility once you are here asking around.
Plenty of dock space, Crown Bay Marina, Yacht Haven, possibly Sapphire Marina.
Plenty of anchorage room in different areas if you are aboard, and maybe move to a marina for times you are off island?

You might post this on the USVI forum for some different responses.