Please don't worry about the trash. I'm a really peaceable person, and I've even been ready to give a snappy answer to that board (and I can guarantee, here comes one back to me}. You won't have a problem, trust me. The sea grass comes up every day, but most hotels clean it right up. There is some debre that blows on, but they try to keep that up too. Unless you are way south or way north, they keep it under control. And even in both those places, its not dreadful. Jeesch!
Last trip I saw a local guy picking up trash in front of the cemetary, as that is probably not monitored by hotels. I gave him a piece of glass I had just picked up and seriously thanked him. But, it was only one piece of glass, that's all I had to pick up.
This has become a great to-do about a not so big problem. I can't even imagine why it has taken on this magnitude. I kick off my shoes the day I get there, and sure wouldn't be doing that if I had to crawl over trash. Jeesch!
Re the weather, needless to say that's up to nature. My guess, it will be fine. I don't know a darn thing about weather patterns, but apparently it is affected by the weather in the north. As our weather settles down, hopefully there's will. I was there 2/13 to 3/4 and it was 82 - 87 degrees every single day. Blue skies. No humidity. Had some big water roughness, if you dive. The only time it rained was once after we were already in bed. A couple years ago, we got some chilly weather, but we came earlier in the year. Obviously, some people got it this year, but summer is coming on. And, as always in travel, the longer you stay, the better you will get the pleasure of how it is.
On your computer, just check the weather site. That will tell you what the present weather is, snd give you an idea of what it is expected to be. It may rain, but it will probably be 85 degrees. I can live with that. And, please do check good old Lonely Planet, and no I don't work for them, but they will give you the best idea of what you will find.
Not to worry. Just go and have fun. Unless you really love fancy places, you will love Belize. Be advised, it is laid back.