+ another for Tres Pelicanos.
Without a doubt, If you're staying at Hotel Cozumel and are looking for a dive op that addresses all of your wants (with the exception of an afternoon 1-tank dive as they run another 2-tank dive in the afternoon) you should put
Tres Pelicanos Dive Center on your list and, in my opinion, at the top of that list. Read my latest review of Tres Pelicanos posted on Trip Advisor from our Dec 2015 trip. After diving coz for 14 years of Diving coz I can't tell you 3P's the absolute best as we haven't been diving with all 100+ dive ops on the island but I can tell you it's the best we've ever found and certainly aren't looking for another.
As far as planning, you just vist their website and send an inquiry with all your questions/concerns/dates/whatever... Jeanie will immediately respond... usually in just a few hours! Yes, the more days you book the cheaper it is per day.
If you go back a page on this forum and read the replies to "Cozumel-going solo where to stay" you can kind of start where someone else left off and see all the responses to his post regarding places to stay (although you're already booked) but more important the dive op recommendations that showed up in that thread. He ended up selecting 3P's.
I think you'll find 3P's shows up everywhere as a top recommendation that should be on your list.
Wish we were going to be there when you are but Coz isn't on our schedule again until December.
Stay wet!