Hey shangrl, ok firstly take a deep breath
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Lol, ok I've only been on a few dive boats in terms of the size and class that you're referring to.
Letting the DM know that you're a newbie is advisable and makes things easier for everyone. You should also let your buddy know that you're a newbie.
Generally I only put on my wetsuit halfway until i'm kitting up on the boat and about to jump off.
And just to confirm your question, yes believe me, you will get hot pretty quickly in a wetsuit.
Dive brief generally would include details such as max depth, dive time, history of the dive site and the route that you're taking and maybe marine life that you'll likely see.
Some things to keep an ear out for are instructions for returning to the boat and the type of entry necessary to get off the boat. Generally with large boats you do a giant stride entry with smaller boats backward rolls or forward rolls are the norm.
Generally divers use more weight in saltwater due to the fact that it's more buoyant (consequence of all the dissolved salts in the water). Can't give you an exact figure on how much weight you'll need for saltwater, ballpark figure of maybe 9-10 pounds??
Use whatever method you're most comfortable with for storing your weights.
Weight belt or integrated weights are fine with most.
And finally just try to keep in mind what you were taught in your Open water course and have fun!!
I'm sure others will chime in with possibly more useful and detailed advice :14:
Where are you going by the way?