I'm trying to create my own homebrew campaign. I am running into some difficulties with putting classes and things into stats, numbers and probabilities. I would like help in figuring some of this stuff out if possible.
And by "campaign" you really mean "Making an Entirely New Game from Scratch"?
If so, then my advice is to go invest in a copy of Dungeons & Dragons 5e (just the Players Handbook, Monster Manual, & Dungeon Masters Guide), & read that to see how this is done.
Or any other existing RPG since there's no one exactly correct way to make these things....
I'm unsure of your question. Are you asking how prevalent certain classes/races/etc. should be in your setting? Ratios are great for that. Or are you asking which classes/races/etc. you should include as playable?
Or as you asking how to make all of those things from scratch?
As much as I enjoy creating campaigns, I wouldn't attempt to make a D&D-like game myself. Too much work when suitable products already exist. And there's plenty of clones with plenty of variations on the subject.