DenseFilm500

I heard before from my professor that emulsion paper is archival and can last for decades, but I was wondering if there are certain conditions that must be met for the storage of the paper that effects its hypothetical shelf date?

I'm curious as to why developer needs a specific temperature before it can be added to the negatives, will it not work otherwise or will it just be less efficient?

I want to understand the process of turning my negatives into pictures and something that always confused me was how fixer works, i always get complicated answers, so if someone could try to explain it simply so i could understand i would appreciate it greatly.

My film have consistent light leak around the edges and has is unusually dense, I'm using Tri-X 400 film black and white negatives with a Vivitar v3800N. I'm pretty sure the mistake is somewhere in the processing stage, since ive gotten good negatives before, but its a rare occasion. Any help would be greatly appreciated.