SXM-Anguilla-SBH is one of our favorite bareboat trips. We just did our fourth one in these islands last May. We charter out of Oyster Pond so our routing is a little different. Last trip went like this:
1st night at Grand Case
2 nights at Road Bay
1 night Crocus Bay
3 nights Gustavia
You might consider Grand Case your first night if you can get pre-check out. Not sure if you can do that from the Dutch side. I wouldn't let Tuesday night drive your GC decision. It’s fun just about any night.
We spend two nights at Road Bay so we can spend a full day on the beach at Shoal Bay. Grab a taxi. It’s beautiful.
After leaving Road Bay we picked up a park mooring at Little Bay and BBQ'd snorkeled and chilled. Then motored around the corner to Crocus for dinner ashore. Snorkeling at Little Bay is just OK, but a pretty spot to hang out.
Next day we sailed around the east end of Anguilla all the way to SBH. Lunched at Columbier then to Gustavia. Usually we overnight in Columbier, but this trip our college age kids wanted to spend more time on SBH. Thus 3 nights at Gustavia.
SBH is one of our favorites, but I was disappointed in the mooring conditions in Gustavia this time. They've allowed so many locals and live aboards to moor outside the harbor, that its tough to find a good place to anchor that isn't rolly.
You've got a fair amount of sailing in your itinerary. Keep in mind these anchorages are farther apart than the BVI. You'll probably get plenty of sailing in on your passages, let alone day trips to snorkeling spots.
We eat dinner ashore every night. Let me know if you would like recommendations.
Enjoy. I'm jealous!