Don't know the resort, but you've got a good dive op. I dove with Tank Ha in January and I would go with them again. I've done the cenotes twice. The first time, I only had less than 25 dives logged. My buoyancy control was OK in the ocean, but questionable in the cenotes. It can be pretty tight in spots and you always know you have to stay off the floor so you don't stir up silt and off the ceiling, so you are always thinking about it, which of course makes you very conscious of it. Air consumption was also an issue, because we used the rule of thirds - one-third of your air supply out, one-third to come back, and one-third in reserve. I had to call the dive on the gas supply. There was a lot to think about and I was kind of nervous, so I was huffing and puffing.
The second time was about 200 dives later and after becoming a Dive Control Specialist (the SSI version of a dive master) and instructor. Needless to say, I was a lot more comfortable and enjoyed it a lot more. The first time, I thought it was interesting, but wasn't sure I needed to do it again. The second time, my interest was up because I knew my skills were much better.
Now I'm not saying that you need to be a dive master or have any certain number of dives to do the cenotes, and you may be able to do them successfully with minimal experience, but it's largely a question of comfort. To really enjoy the cenotes, you have be be really comfortable with your buoyancy control and air consumption - to the point that it is all pretty natural and you don't have to be consciously attending to it constantly. If you are really comfortable, go ahead. If you are not really comfortable, think about it. You may not enjoy it as much and it is certainly no place to get freaked out.
