Hello Rei_Unit, I'm LG ^_^ Hope you're having fun here, and stay awhile
To answer some of your questions,
A)I believe blue boxes means it's an active thread while flaming pieces of mail means it's a popular (or "hot") topic. I think gold boxes mean you've posted in an open thread and flaming mail with a black circle means you've posted in that popular thread ^^
B)Not necessarily. Posts in certain forums will contribute to your post count, and some wont. I believe they say somewhere around the title if they don't.
C)You can learn a little more on userbars here, and how to make them and such (If you make one yourself tho, you'll have to host it yourself). There's sites out there that have already made bars ready for you to put together, and there's even a site that will animate and host them for you too~ (at the moment, I can't remember it at all.. I'll edit this when I do though =))
You can PM me whenever, I always welcome chatting and questions and whatever ^_^