A Small Orange and SiteGround are the two I hear about often when people talk about top notch shared hosting. Note: ASO is now owned by a big ol' webhost conglomerate (EIG) but apparently they're still pretty good.
I am not terribly impressed with Hostgator. No major issues so far, but when we were scanning for vulnerabilities we found they still hadn't patched the BIND vulnerability on our shared host. This happened about a week ago, so they let their servers sit around unpatched for about a month.
I do strongly recommend using Linux if you're wanting to do web hosting. Few places offer Windows hosting, and support/tutorials for IIS webservers is severely lacking compared to Apache or even Nginx. On top of that, most places offering Windows hosting does so at an increased cost as you need more powerful servers to make it do the same stuff Linux does. Even with Windows admin skills in the bag already, it's quite possible that you would end up spending more time and money learning how to effectively serve websites + forums on Windows than you would learning how to do the same thing on Linux and Apache or Nginx.
Depending on how fancy you want to get, you could really jump in headfirst and sign up somewhere like Digital Ocean for a VPS. This is almost guaranteed to be faster than what you would get with a shared hosting setup, and you have root access to the server to install software as needed. Their smallest $5/month server is more than enough for a website, even a CMS like WordPress, and it could probably run the forum software as well as long as you don't have a ton of people using it all at once.
Speaking of forum software, Vanilla Forums is a nice system with a free open source edition!