Usually we've also stayed overnight at the Emerald Beach. This works well:
- After turning in the boat, take any available ferry to St. Thomas. No worries about issues such as the ferry running late.
- Nice restaurant and bar at the Emerald Beach.
- Nice beach and swimming in Lindbergh Bay.
- Close to the airport. It's walkable, but we've always taken a taxi because of luggage.
At least one time we had the minor annoyance that our room was not ready for the first couple of hours after we arrived.
We did thing differently on our most recent charter.
- Spent the last night of the trip docked at the charter base in Road Town.
- Caught an early ferry in the morning.
- Had a relaxing lunch at the French Quarter Bistro.
- Taxi to the airport in plenty of time for a late afternoon flight.
This packs more into one day and is a little riskier if anything goes wrong, but it went smoothly. In your plan you won't have the boat for that last night. Perhaps others here can recommend a Road Town hotel -- maybe Maria's (which is very close to the ferry terminal). Or you could stay farther away, like on Cane Garden Bay, but then you'd have to get a taxi early enough to catch the ferry.
Dan