I'm not sure how much undergarments I'll need. You said not to underestimate the neoprene, do you mean that it does a good job insulating or that it doesn't do a good job? This suit is 7mil but it seem thicker and heaver than my 7mil wetsuit. Might just be because there are socks, and neck and arm seals, and a really heavy zipper. I didn't get cold IN the water with my wetsuit. There was a little chill when the water first ran down my back, but after that I was fine. So I don't think I'll need much undergarments with this drysuit at Blue Hole. Now when we start getting back into 43* water in the mountains, that will be the test! The "fleece" your talking about at Walmart...is it like the old fashioned long underwear? Or like warmup pants/jacket, or more like sweats?
I think the neck is a bit tight. I didn't get any directions/information with this suit, but have read that some "stretch" the neck seal over the end of their tank. Did you have any problems with your neck seal? Also, it came with a huge duffel/backpack bag, but I'm not sure how to store it correctly. It came folded, outside the bag, in the box, but I've read that you should not fold neoprene, or you will weaken the cells at the folds. I read where some drysuits you roll up, but not sure if that was just for trilam or included neoprene also. I thought I'd get a "care and feeding" guide for the suit written by O'Neill, and maybe even a warranty card. But there was no paperwork in the box at all. .
I won't try it on a night dive for this first dive. I want to get used to the feel, and the feel when there is too much air, not enough, and see if I have the problem of "feet first" (I kinda doubt it, since I don't think there will be enough air in the suit to cause that problem) and practice maneuvers to get out of that condition if it does happen. I'm planning (as of right now) not using it for buoyancy adjustment- but use my BC for that. What do you do? (Ron mentioned that you bought a neoprene also). .
Since there are a number of experienced drysuit divers willing to teach and give advice instead of requiring you to take the drsuit specialty, you may be able to get the info that you need and start enjoying your new drysuit.
I really think that you need to try the suit in a pool first. You can work on weighting, trim and bouyancy. You will figure out how much air to add to offset squeeze, and you will figure out how to dump air without rocketing up from an obscene depth.
Stretch your neck seal over a tank and leave it overnight. When you put the suit on, roll the neoprene inward, and keep rolling it down until the opening fits your neck nicely. You usually would NOT trim a neoprene neck seal.
Wrist seals are rolled in and back until the opening fits your wrists nicely. The openings get wider as you roll them back to the inside.
Wear snug fitting long johns. If there is excessive material, or material with fuzz, it can prevent even air distribution inside the suit. You will have to decide on thickness. I purchased some heavy polypro long underwear, top and bottom, at an army surplus store. The price was right. The insulation is excellent.
Get a drysuit hanger with extra wide shoulder support to hang your suit while it dries. Then store it by laying the suit on its back, then turning the toes inward on the booties and loosely rolling it from the booties up. When you get to the top, wrap the arms around the rolled area. Keep the zipper waxed and keep it all of the way open. When the arms are wrapped around the bulk of the rolled suit, it keeps the zipper in a nice relaxed shape. Put the suit in a duffel bag and store it in a cool dry place.
Get the appropriate fins. Scubatoys has some closeouts for less than $40.00. Also, you can get a pair of neoprene booties a couple of sizes larger than your regular ones and wear them over the drysocks. Then they won't slip around and you don't have to tie them on with string.
Work with Ron and your friends at Blue Hole on bouyancy and some drills like getting out of a situation where you are feet up and ascending.
Have fun!