For example, one of my schools says Required: 0, Allowed: 2 on common app. (University of Oklahoma) Does this mean I should go out of my way to submit 2 LoR or not? What about if it says Required: 2, Allowed: 3… Is there some place where I can read up on some flushed out policies on this because frankly it’s kind of confusing, especially when a lot of college websites just say “Letters of Recommendation” under their requirements and give no specifications as to whether they require certain teachers writing them or how many.
My head 
Google “University of Oklahoma Recommendation Letters”
That simply means you may submit 0-2 for U of Ok, and 2-3 for the other one.
It goes without saying (I hope) that you will submit any number of LORs that are “required.”
For any particular school, if none are required, but some are allowed, I would submit at least one LOR, assuming you have a teacher that can/will write a good one.
In general, you would not submit more than the “required” number, unless you have an unusual and outstanding additional reference. Example: maybe the school asks for 2 recs from teachers of core subjects, but allows additional recs. If you are a star athlete or musician, a rec from your coach, instructor, or mentor in that specialized area would be a welcome and worthwhile additional LOR. A third rec from an academic core teacher, not so much.
Your goal should be to boost your app in any way possible. So if none are required, but up to two are allowed, you would be best off submitting at least one and ideally two. Same goes for optional essays. IMO, optional supplementary essays are never really optional.