Well, what are your questions about feasibility? You can certainly dive the Yucatan in October -- the weather is likely to be somewhat rainy, and there is still the risk of hurricanes, but it is past the peak season for them. Unlike Florida, the Mexican caves don't flood out, so even in rainy weather, you can dive them and the viz is still good.
If you have not been to Mexico before, it is not a bad idea to engage a guide. It's not that you need help IN the caves (although some of the main lines are not easy to find) but more that the locations themselves can be difficult to describe, and knowing who to contact and how to get keys and who to pay can be kind of complicated to sort out by yourselves.
Most of the commonly dived caves are located between Puerto Aventuras and a few kilometers south of Tulum. Flying is into Cancun, and you can rent a car there, or if you are staying at a resort, it may run a shuttle (they generally charge for them). If you are primarily cave diving, I would say you want to stay south of Playa del Carmen, or your commuting will be substantial, although there are all-inclusives in PDC that have very good prices in October, as it is off season.
There are a couple of cave diving shops with bed and breakfast facilities in Tulum, although when I investigated them, the costs ran higher than what we pay to rent a condo and tanks up in PA, where we stay. But if you would like some more information about cave diving there, please feel free to PM me or put them in this thread. There is also
THIS thread that may give you some additional material.
