ASA400, Your plans for packing your dive items sounds great and as others have mentioned you most likely will not have any problems with TSA regarding your gear. However, just a heads up that there are some different rules which apply for the return trip home. When leaving Mexico departing rules and regulation are no longer "TSA" , but a Mexico Agency and therefore do not have the same exact rules. In general, the policies for dive gear are the same with the exception of weights. Should you plan on taking weights along, although my guess is most people use the weights provided by their dive op, you are able to take them into Mexico in your carry on luggage but you are not allowed to depart Mexico with weights in your carry on luggage and and therefore must be transported back home in checked luggage. I used to have to deal with this when I would carry my on soft lead weight as my dive op did not have them.
Other than dive weights there are other items as well as different rules and policy that are different from (USA) TSA. If you have not already, please do check the STICKY-Arriving/Departing the Cozumel Airport- A Guided-Tour which is located at the top of the Cozumel Forum. Just scroll to entry #1 which is the most current and updated version. I will warn you, that it is a bit lengthy, but it chocked full of info that several of our Scubaboarders have contributed. So, perhaps, set aside a little bit of time, get a cup of coffee and check it out.
Best Wishes to you for your upcoming trip and Have A Great Dive Vacation !
Double S