Welcome to Key Largo! If I can answer any of your questions, please shoot me a PM.
Come on down, the weather is awesome and the diving is great. There are plenty of affordable accommodations. I recommend that you check with the dive shop you will be diving with. Many have contracts with a few hotels and can get you much better rates than you can get on your own.
There are almost 30 dive shops in the Upper Keys so there are lots of choices.
Just something to consider: The last Wed & Thurs of July are FL's Lobster mini-season. It doesn't affect most dive shops that dive within the sanctuary, but it does impact local traffic and hotel rates are usually at a premium.
Depending on the size of your group/family you might consider condos which offer the ability to prepare some of your own meals.
I also recommend you do a search here in the FL forum for Key Largo as this is an often discussed topic and you will find more information ranging from dive ops, training, accommodations, eateries, dive sites, diving conditions, and much more.
Let me know when you come down and maybe meet up for a
.
Elena