knee pads will definitely prolong the life of your suit. Front Zip suits are much harder to put on and take off. Ankle and wrist zippers make it easier to put on but then again, that depends on the thickness of suit. If it is low to med thickness, dont bother with the extra zippers -- just something else to break and allow a faster transfer of water decreasing the suit's potential to keep you warm.
I dont see a need for elbow pads but that depends on the type of diving you do. If you crawl around or lay on your elbows to get a good photo, then they would be worth it.
Pee Zipper I see no use for. And for the record, I DO NOT pee in my wetsuit and think unless you are down a very very long time, you shouldnt have to. BUT, if I had to wear a heavy suit where putting on and taking off was a super duper chore, maybe I would have a different opinion. I just usually wear a pretty thin suit so putting on and taking off is not a problem.
Hey, IF, and that is a big IF, I were to get a custom suit, I would absolutely get a custom color or pattern.