Some of my most exciting dive trip memories have been due to surface interval and boat trip happenings. Whale sightings, snorkeling with dolphins and white tip sharks, mobula rays,whale sharks. Keep your eyes open and you see a lot of things. I always have a snorkel/mask and fins at the ready, assuming the captain allows. Don't fall asleep and assume your trip is over or hasn't started, just because you're above the water or you may just miss half the fun!
As far as questions about what to wear-at those temps, assuming you'll do an average 2-3 tanks a day, I'd wear a 3ml full suit with a 1 ml tropical beanie. I prefer a full suit because it protects me from stingie things and seems to keep me warmer. Also, I always wear a Lycra skin, which I buy for about $25, in fact, I paid $12 on sale for a new one recently. This serves a few purposes. It helps the wetsuit glide on, especially when its wet and yucky, it protects me from the sun on surface intervals because I'm very fair skinned, plus, it dries very quickly so that I can strip off the wetsuit and add a jacket on top, and be much warmer than walking around with the wetsuit. I never travel to the tropics without a jacket for surface intervals,btw. And,sun hat,preferably one that can stand to be crushed in the packing.
Lots of good wetsuit sales right now, since it's pretty much end of season in most areas.
As far as places to stay-if single, all inclusive in Cozumel would be my choice. They are fun and usually include alcohol, so if you want to socialize,the bar will be hopping. I remember, the last time I went to Cozumel, having a very fun time hanging out with a bunch of other women ( I'm married so I wasn't looking for guys) and having a very fun time. My ex-husband was pretty antisocial so he went upstairs to watch TV so I was on my own, basically like I was traveling as a single woman. The all-inclusive is almost like a small city with several bars, restaurants and snack areas. Entertainment, it really is a fun place to hang out after diving. It feels much safer than walking the town yet still with plenty going on. Not like the typical hotel with a single, dark and quiet bar area. Think more like a Las Vegas casino, without the gambling. Or, maybe a cruise ship, although I've never been on a cruise ship.
If you don't enjoy boats because of sea sickness, have you tried a patch? Sounds like you don't enjoy boats so I was just wondering if its because you get sea sick.