You don't have much time on Tortola but I'd recommend stopping to see Egbert at the North Shore Shell museum, do a beach day at Smugglers or Cane Garden Bay (better for swimming). For meals, the food is great right at Sugar Mill, lunch or dinner at Indigo Beach House in Cane Garden Bay, Da' Coal Pot is nearby for dinner, the tuna at Quito's in Cane Garden Bay is also great! I like the atmosphere and food at Long Bay Beach Resort which is also very close to you.

No need for a water taxi to Scrub. You can't be picked up at Sugar Mill anyway so by the time you get in a taxi to go to a dock you might as well just taxi to the Scrub Island dock near the airport and save huge $.