If you're enthusiastic divers I'd think about getting your own analyser. I don't know whether Chuck & Robbies have analysers to use, but I do know that many shops here don't. When I had my tech center I had 3 or 4 analysers for customers to use, plus others for in-house use, but they work out quite expensive if they're not used much. I agree you should always analyse your nitrox, but with a continuous production system such as Amigos operate they can guarantee the mix so long as nothing's gone wrong in the production process or with the equipment. I used to bank 32% and 36% and I knew that those mixes were accurate. The only time that failed was when one of the in-system analysers started to fail, and the chap running the system knew immediately as he started to get different readings from two analysers that should have read the same.
I normally suggest people do the first dive on air, as typically here it may be getting a bit deep for 32%, and subsequent dives on nitrox (32%, being the only mix available here). If you customarily "push the limits" then you'll find you'll have to do the second dive on nitrox to avoid going well beyond no-deco limits, and if you're doing three dives it'll be absolutely essential. If you're trying to economise then I'd usually do the second dive on nitrox and revert to air for the third if necessary. On the BH day do both the second and third dives on nitrox. Even if you're not permitted enough dive time to approach the limits, you'll probably feel much fresher at the end of the day when it comes to going out for a meal.
If you're doing six days of diving and the first dive always on air, you're not talking about much extra cost for nitrox. Look at what the whole holiday is costing you and get it in perspective. Incidentally, most people here charge $10 plus sales tax, which makes it around $12 per tank.
As you're relatively new to this sport and are clearly enthusiastic, why not start measuring your gas consumption and relating it to your dive profile? Calculate your SAC several times during the week and see how they compare. Knowing a typical SAC for you is one of the most important factors as your diving advances.
I hope that as enthusiastic divers you have DAN dive insurance? I would always check where the closest recompression chamber is, how to contact it and how to get to it. And also check with them how they operate. I know those answers here in San Pedro, but if I were to go to say Roatan that would be the first thing I did, before I ever went diving. In general I'd check that whatever your dive operator should be doing to protect your interests they are actually doing. Chuck & Robbies are a good dive center and I'm sure they do things properly (ditto Amigos), but I know of two cases recently where people thought they were given added protection by their dive center contributing to the local chamber, only to find very much to their cost that the contributions hadn't actually been handed over and the added protection wasn't in place. Check with the chamber if in any doubt. Unfortunately this isn't monitored by the BTB or any other agency here.