No problem! If your youngest daughter is getting married then you're not a youngster yourself
. All the more reason for being conservative. Remember, tables and computers only give average information for average people. I don't think I've ever yet met an "average" person. As you get older it's all the more important to follow basic safety rules, and the most significant of those is to keep well hydrated. The evening before diving I'd steer clear of alcohol, or at any rate only consume a small amount. I never drink (alcohol) in the 12 hours before I dive, but then I know alcohol affects me more than most as I had hepatitis A many years ago, and it's a life sentence.
I can't find now whether you said you were nitrox certified. I just rather assumed you were from your mention of nitrox. Assuming you are, I'd tell Ched to get in three tanks of EAN32 for you, even though your DM probably won't be using it. If you're not nitrox certified I'd rectify that asap, and I wouldn't do four dives a day until then.
When I had my dive center all my staff were required to use nitrox on all dives except deep ones - one of the "hidden" costs that make some centers charge more than others. They were all also covered by DAN insurance, something that is not often the case here. I trust you have dive insurance as well as trip insurance? If you don't, please go to the DAN Americas website NOW and buy it. It costs the same as between two and three dives for a year's cover. I forget what the DAN Americas cover categories are (mine is with DAN Europe which is completely different) but from what I remember get the second from the top cover, the one that also covers against non-dive accidents while you're away.
Whoever you dive with in Belize, make sure they contribute to the recompression chamber (US$1 per dive). They may or may not pass that charge onto you (I absorbed it, which was another reason I had to charge higher prices). Regardless of whether you pay the $1, if the chamber doesn't receive agreed contributions from that center you will not be covered by them. The $1 makes a tremendous diference. There are four financial states to arrive at the chamber in. If you have no insurance and the $1 hasn't been paid, you will be required to pay the chamber the full amount at the time of treatment or at any rate before you will be allowed to leave. This can be a massive amount of money, especially when you remember that after chamber treatment your airline may refuse to carry you for a week or more.
The second possible state is that yiou have insurance but the $1 hasn't been paid. In this case you will be billed and will have to pay before you leave, and then you will reclaim from your insurance company.
The third state is that the $1 hs been paid but you're not insured. The chamber charges will be capped to a far more reasonable level, but you will still be required to pay before you leave.
The fourth and greatly most desirable state is that you do have appropriate insurance and the $1 has also been paid. All you have to do is sign appropriate documents - you won't be asked for a cent.
Don't forget that in the event of chamber treatment being required there will be many other costs. You won't be able to leave, certainly during your treatment and quite possibly for up to a week after. Your family won't want to leave without you, so even if the airlines reschedule you for free you'll have added hotel & living costs, to say nothing of people not getting back to jobs & family.
All this is not intended to frighten you, but to impress upon you the absolute foolhardiness of diving without good dive insurance. If I'm here when you come I can relate some stories to you over a beer!
You describe your new computer as being "air integrated". I imagine that these days it will be nitrox capable, so that "air" is misleading? You need to learn in depth how to use it, focussing on two areas - how to set the breathing gas for each dive (and if you don't, what it defaults to), and what information it displays underwater. On the dives you need to pay the most attention to the no-decompression time remaining, which will generally drop during the dive. As you're still a basic diver do not be tempted to go into deco, as you don't yet understand what issues that raises. Once your "no-deco time remaining" drops into single digits, go a bit shallower until it stops dropping. If it continues to drop you need to go even shallower. Keep an eye on your DM and try to stay in visual touch with him, but look after your own interests first.
If despite your efforts the computer goes "into deco", you need to go way shallower, up to maybe 30ft or even less, until the "deco" clears and the no-deco time starts to rise again. Your DM should be aware of what is happenng and the group should by then be in shallower water. Once you are in deco the computer will probably show the "time to surface" rather than the number of minutes of deco - check with the manual.
If you have gone into deco on a dive and it wasn't the fourth, I'd give serious consideration to calling it a day. If you decide to dive again you MUST use nitrox and stay well away from the no-deco limit. At the end of every dive, and especially one you went into deco on, you need to spand at least 8 minutes at your "safety stop". The longer the better, but treat that as the minimum. Do not be hassled into surfacing earlier. After a deco or near deco dive, take off your scuba in the water and climb into the boat without it. It is the very worst time to exert yourself. Don't drink any alcohol for several hours. When you shower, have a tepid one - don't stand under hot water until at least 2 hours after your dive ended.
I hope those few tips help.
