you should start off by going to Playa Del Carmen to fish. it's a 45 minute drive and way better than Cancun. i'd call the folks at Cozumel Charters and see if they can accomodate you.
http://www.fishingcozumel.net/. they were very helpful when i called and booked with them, although i took my own boat. fishing was great and the capt and mate were fantastic.
I haven't fished with the following group, but they have been recommended to me before:
http://www.captricksfishing.com/. you may want to try them too.