First, pack cash and patience. Once you leave the US, a 'fast' fuel stop is about an hour, but it can easily stretch to two. You are on 'island time mon'.
Each stop requires customs and immigration in and customs and immigration out, oh and then you need fuel and the usual personal stop items. Also, it can often be wise to pay in cash (but don't expect change so bring small bills). I've seen it take 30 minutes to successfully run a credit card.
Florida to Virgin Islands could be two stops or one, especially in an RV-10. I used to be a two-stop person, but that changed after enough times of dealing with fuel stops in the islands. These days, I'd rather slow down so my fuel burn will give me the legs to keep well above required fuel reserves
and make fewer stops. Now, that one stop is going to be Provo in the Turks if you go that route. If I recall correctly, last time they charged us about $75 for an FBO fee, but that means they will hand deliver paperwork to customs and immigration and keep things moving. I'm not normally one to suggest paying FBO fees willingly, but in the islands the hassle and time it saves is worth it.
1. Get your customs sticker, https://dtops.cbp.dhs.gov/
2. Get your 12" N-numbers
3. Fill out and print 3 general declarations forms for IN, and 3 forms for OUT at each point of landing. So, for a stop in Provo, you'll need 6 forms. It's much easier to have these filled out before you leave. If dates are flexible, just leave that off and fill out as you go.
4. Get your EAPIS account. If you already have one, confirm you can get in. Don't wait until a day before. You'll surely have some problem if you do. Complete an EAPIS for each time you cross the border. If going out of Florida and into the USVI, it'll be one report for the outbound leg and another for the inbound leg. I can't remember how early you have to file that, but I usually just did so a day or two before in case dates changed. (That's assuming you know you can get into your account already.) Don't worry about the exact timing on the EAPIS filing. Estimate the times and move on. What I've been told is that as long as the dates are correct, it's all good. When it asks where you're going to cross the border, you can say 15 miles southeast of KXXX airport. It doesn't have to be extremely precise.
5. Get all of our frequencies together on one page, in advance. Relying on charting can make you crazy. Think about flight service, ATC, towers, ground, FBOs, etc. There are places along the way where ATC will tell you good-bye, and contact this frequency in 30 minutes. At least at 12K or so. Surely that isn't the case at higher altitudes, but I don't know where that coverage would start.
6. Get the direct phone numbers to customs at the US airports where you will land. Call them at the fuel stop prior to entry with an updated ETA. While there are some cranky customs folks out there, most I've dealt with are good people. I had read a lot about don't miss your customs window by more than 15 minutes or things could get uncomfortable. What I got on the phone from actual customs officers, it was more along the lines of 15 minutes before to 30 minutes after. So, don't fret about that extra headwind.
7. If you choose to follow the Dominican Republic coastline, working with ATC can be challenging. We affectionately call it "The Impossible Zone". Don't avoid it for that reason, having land close by is comforting, but just be ready. Often times, on the first call up, they basically want your entire flight plan - departure, arrival, souls on board, etc. Just be ready for it. Traffic calls are also interesting. They don't call traffic at 12 o'clock, 2 miles. Instead, they'd provide the other aircraft's distance from a VOR and you have to figure out the relative position. While they are supposed to speak English when one is on frequency, more than once I've been called out as Quatro Ocho Dos Dos Carlos. Again, just be ready and it'll be worth having land within gliding distance.
8. When back in the US, taxi directly to the customs box outlined by the red lines. We didn't take everything out of the plane (left tool bags, tie downs, diving gear and such) and just took in our main bags. Of course, that could vary with the customs station.
9. Always file, open, and close flight plans. You'll need a squawk code coming back through the ADIZ.
10. Most importantly, Have fun and be safe!