Personally, I enjoy having lore, but I usually do a decent chunk that sorta establishes the flavour of the RPG, and stop.

Then I let the players come up with their own thing and work it into the universe.

"Too much" for me is when players get too confused and can't really parse it all. When it's too much for them to properly enjoy. An RPG is essentially a game where chuckleheads get together and do stuff for fun. If it gets in the way of fun, then it's too much.