Simon
Most Hotels open in March, in fact there are several which are already open. There are a handful of Hotels (normally in quiet resorts) which may not open until May.

In reply to your question, I don't know enough about all inclusive Hotels, but there are others on here who do. If you are thinking about DIY, may I suggest you take a look at http://www.Skyscanner.net which will give you details of cheap flights from Newcastle, Durham etc etc.

Hope you find what you are looking for.

Cheers

Adam