Good advice.. I'll add
If your starting to feel the lower back in squats and the such, your lower back could probably be the limiting muscle in the movement and therefore it is going to feel like it hurts or is umfortable first in the muscles your using. Your issue could just be a weak lower back that you need to work on strengthening for a bit before hitting those numbers which cause the discomfort.
Personally, I have tried wearing a belt 2 times in my life. Once when I was 16 and didn't know any better. Thought it was part of being a lifter lol... And I tried one again when I was about 30 beause I wanted more support in my squats. I used the belt for a couple work outs in both cases. In the first care, it was stolen from my gym.. And when I was 30 I stopped using after a couple lifts because it wasn't comfrotable and I also thought "why use a belt when I don't need the support".. My thoughts are, by using a belt (too much), you could cause your body to be underdeveloped in a way. The belt releives some core muscles of their duty in a lift. This in my eyes isn't ideal. I can see the benefit of a belt on your 1 or two heaviest working sets, but any more then that I think your robbing your core of developement. Let your body develope in unison.
A belt works by increasing your abdominal pressure inside. This causes your core to be stiffer in a way. This makes your core not want to bend as much and therefore makes it easier for you to suport the weight with your core.
Elbow wraps I think work by making it difficult to fully bend your elbows. So as you lower the bar in a press, the wraps dont let your elbows bend in as easily therefore they are resisting some of the weight.. so they work slightly different then a belt.
A belt won't do fuck all for back pumps imo.... Thats the dbol I'm guessing. Huge guys get back pumps all the time from just holding themselves up.. I don't think your in this category though.
I don't like knee wraps either. I was taught they secure your knee cap in place too much during a movement which can cause damage. A knee cap is supposed to slide up and down through a knee bend. I know many disagree with this, but I did my personal training course through a top trainer and he taught us not to use them for those reasons.
I am a big pusher of using wrist wraps for pulling movements. Your grip strength will always limit your working weights on pulling movements when you beome more advanced. I know some guys will stick to no wraps as much as possible and only use them in their heaviest pulling movements, these guys generally have very well developed forearms. I use my wraps too much and it does show in my forearms compared to upper arms.