The other posters have provided plenty of good info.

Alona Beach is great and IMHO the whole Panglao / Bohol experience is a Philippines "must do"!

5 or 6 days would be ideal. You'll be able to see teh Chocolate Hills, Loboc River, Tarsiers, etc. on bohol itself. Around Panglao, you'll be able to check out the beaches, go island hopping, snorkelling, diving, etc.

Best way to get there from Cebu is by boat, but you can fly direct to Tagbilaran very easily from Manila.