You'll have a great time. Casa Mexicana is a great location with fantastic breakfast. Santa makes the best omelettes.

Hard to go wrong with Aldora.
Random tips, a light rain jacket if you have one. Aldora provides waterproof fleece lined jackets for after diving if you're cold. I bring a long sleeve shirt or light sweatshirt at night but for most people it's not needed.
For Casa Mexicana breakfast, try to get down there early, say around 6:45-6:50am. It will give you a little extra time since Aldora leaves pier at 7:30am. Sometimes they don't always have everything ready to go at 7am but you can usually grab coffee, juice, cereal, etc. I like to make sure I leave by 7:15-7:20am. It's only a ~4-5 minute walk from the pier so you have plenty of time. They're not going to instantly leave you at 7:30am but you may be last one on boat. Not a huge deal -)
At Casa Mexicana, you're in walking distance from a lot of great restaurants and bars. Dont forget to check out Los Otates for tacos, Thirsty Cougar for margaritas/food. La Choza for food. Lots of other options equally good but these are pretty close to you.
With Aldora if you've never used steel tanks before you're going to need a lot less weight than you think. DMs are generally good at helping with this but you can expect to take ~6-8lbs off your belt compared to what you wear with an Aluminum 80. Very rough estimate but some can expect to dive with very little or no weight at all depending on exposure protection.
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