Welcome to the Q&A Forum

I have wordpress blog installed on my Domain and now I intent to start a Forum. I understand that the content on the forum would be thin-content which may attract Google Penalties. So, would it be wise to start the forum on a sub-domain to avoid any penalty. My query is:- 1. If the content on the sub-domain is thin, can it impact my main domain as well. 2. Should I install the forum on a sub-domain or an entirely different domain so as to avoid any penalty? My preference is a sub-domain provided google does not levy any penalty I also intent to display RSS Feeds of the Forum on the Home Page of the Website.