Almost 2 years and the Kubi rings are a dream. So those stay. I have only done off the peg sizing, generally OK but a bit baggy around the calves. Maybe a custom made to measure would be nice some day but for the cost a set of gators are an acceptable fix for me.
There are a few things I did on the current suit that were a result of not liking my first suit. Attached boots. I know a lot of people who only do attached dry socks and put rock boots over them. I had that, I hated it. I tried a lot of things to make them work, but with my feet they just didn't. 2 different pairs of actual rock boots, pair of cheap shoes, even did a set of wetsuit booties once. Hated tying the shoes, laces always coming untied (or were impossible to untie), feet moving around inside the socks or squeezed too much. The wetsuit boots were the worst, I had my foot slip out while the boot stayed in the fin. So attached boots on this suit and they are great. Others will disagree, fine, you don't have my feet.
Another change, lighter material. The first suit was a very heavy bomb proof tri lam. Felt like you were putting on a hard hat suit. Didn't conform very well, didn't pack very well, didn't do much well for comfort.
Pee valve, yes. If I can do several hours in the suit without peeing, I am dehydrated. Not a good thing.
As for undergarments, I have not found the perfect ones yet. make sure they will still be usable when wet, because at some point you will be wet and still want to be warm.
Will only do Silicone seals. I kill latex. With dry gloves, no need for neoprene on the wrists. Have never tried neoprene on the neck. But it should be fine.
And watching others, make sure the dry gloves are installable at the end of gearing up. Stuff like DUI zip seals require you to get out of the suit to get out of the glove. And gloves are going to be the number one place to have a leak.