On San Juan, do your research on your beaches. The Atlantic beaches are rough, but if you go to the east to like Luquillo you will get the beautiful calm Caribbean beach. Also, there is a great little beach bar called Alambique that may be worth checking out. It was great precovid, will be visiting again in Nov, but are still expecting it to be great! Old Town San Juan is definitely worth a visit. Also, I heard the El Junique (sp?) is worth a visit too. Only been to St. Lucia once. We went on a beach excursion - locals will constantly push you to buy their wares the entire time you are there and they kept trying to touch my hands which I found extremely off putting. I would not go back to the beach there unless it was a private beach at a resort. When we go again next year, we will likely go for the Pitons via catamaran, but this excursion tends to sell out quickly too. I haven’t been to St. Kitts yet (going in Nov.) we have planned to do the Essential St. Kitts with Fairview excursion because it was available (we are silvers currently), but our first two choices were the Caribbean Cooks excursion or the Rainforest Hike, but they sold out QUICKLY. 4x4 excursions appear very popular here too. Have not visited Dominica yet (going next year). We went to Barbados pre Covid and LOVED it so much we said we would go back and stay there for a week or more. We haven’t been back post Covid. But we did an island tour excursion and it was AMAZING! We still talk about it! I think the guide is what really makes it. She was wonderful. We did happen to meet a mother daughter while we were there who told us that the island is so nice and safe (at the time, YMMV now) that they just book airbnbs, cook there, and go to whichever beach they want on that day. We will be going back next year, so we are looking forward to it! On Antigua, if you are not used to VERY PUSHY, CERY AGGRESSIVE taxi drivers, I highly recommend going with pre-arranged excursion. This port can overwhelm unsuspecting tourists quickly. Antigua has tons of beaches though, so you will find a beach, just be prepared for the taxi drivers and make sure to agree on prices very specifically. Our first time there, I was prepared and we just got a cab and he took us to a beach and came back for us and everything was fine. But be prepared. I recommend watching Tips for Travellers on YT for Caribbean ports. He gives a lot of very good tips that are especially applicable to Antigua. This year, we have opted to do the Catamaran and Lobster Lunch Cruise. It has gotten good reviews in the past. I happened to find a fairly recent YT video searching this site for this excursion and what ultimately led me to choosing it. Just use the search function. It was a couple and they gave a comprehensive review.
Hope this helps! We love the S. Caribbean itinerary and almost exclusively cruise this itinerary.