I have seen many fliers and such around the city. Is there a set of rules governing being able to do that? I mean to imply, if a character wanted to have a flier put up in game, is there a way to pay for and arrange for that to happen?

Just use the forums.

Notices that are interesting and relevant may appear in-game.

And do we need to pay to account for the costs of posting them or anything? Sorry. Last server had lots of rules covering way too many things and I'm trying not to step on toes. :)

Nah, you don't need to pay for the cost of posting things. If you want to trash a few gold coins to pay for materials, that's fine, but optional.