Fudi, welcome to the site! We're glad to have you. I'm up for a virtual brunch any day. Many players will attend if you serve chocolate, and Montyb will require a pizza.
Your questions touch on topics that I have seen addressed in various hidden places -- in forum comments buried within other topics, in quote comments that you might find by accident someday, and in chat posts that disappear after a few days. The best route to find answers is to check the FAQ tab or to use the Forum search function to find a key word (e.g., "scoring" or "difficulty"). Or just ask, as you have here; helping to orient new players is a nice way for the gang to connect.
Here's what I can offer....
History of the difficulty ratings:
It used to be that the three ratings (easy, average, difficult) were based solely on quote length, which resulted in lots of bad ratings -- many short quotes are actually easy to solve and many long quotes are very difficult. To address this problem, in March 2016, Stephen Ryder (the site administrator, a.k.a. Puzzle Baron himself) collected actual solve times and user feedback data on quotes, and he did a full reassignment of difficulty ratings based on all that data. The results were not perfect -- we still have quotes with wrong-seeming difficulty ratings -- but my experience is that most quote ratings are much more accurate than they used to be.
Here is the forum thread where Stephen announced the change, followed by us riffraff responding with polite appreciation, exceptions, and grumblings:
How scoring works:
This is explained within various other-topic forum threads, but you have to dig for those posts. (It really should be covered in the site FAQs, since it is probably THE most frequently asked question on the site.)
Here's a concise summary that maradnu came up with in one of the forum threads:
Maximum points for Difficult: 450
Maximum points for Average: 300
Maximum points for Easy: 150
For every six seconds, or portion thereof, you lose one point from the maximum.
Note that, because of that "or portion thereof" part, you lose a point after the very first second. So the highest humanly possible scores are 449, 299 and 149.
I agree with other explanations. I'll add that when you hit the Senior Member status, you get to change your title from "Senior Member" to anything you want.
And that's all I know. See you in the quote comments....