1.
There are lots of good hosts out there. I would recommend Dreamhost. Its cheap and you get stuff like unlimited DBs, lots of "one-click-installs" like wordpress, joomla, polls etc. Search on the internet and you will find discount codes up to $97. The have an excellent customer support. They have a really simple web controll panel that is very user friendly. You can host unlimited subdomains and domains.
Gosh, almost sounds like its my site
2.
I would recommend you to learn HTML and some CSS by our own. It isnt really that hard at all. Once youve learned it you are able to maintain your sites easily. If you cant design your own site you can always get a designer to do it for you. There are even some good designers here at PAW (seach the forum). Once he has created you a design template you can add content by yourself and update it with some basic HTML and CSS.
3.
vBulletin costs around $160. That is a one-time payment. If you cant afford that there are plenty of free forums to choose from like phpBB etc etc. As Jordan said it is very hard to open up a new forum without much traffic. Start off with a simple webpage and build up some traffic before you integrate a forum to your site.
4.
To add banners to your site is quite easy. It only requires some basic HTML skills.
Continue to read posts in the forum and you will learn the basics fast.
Good luck!