Thanks skippdastraw,
Your proposal is surpringly simple and makes the reality check:
7:30 - 7:55 VG - RT on Sensation Ferry
8:30 - 10:00 RT - RHK on Aquatic Rentals (assuming modest 30min St John C&I)
10:00 - 10:30 RHK - STT

90 min buffer for Delta check-in !
Although, $370 for 2 PAX total (Cape Air would be only 80% more and water taxi probably 4-figure)
Knowing your ferries in the BVI is key and you are a master.