I am looking to starting up a politics blog and was wondering what would the best aspect be towards going about on it?

I have a decent domain set up for it and the resources, but what about marketing, SEO, Advertising, etc?

Should I set up a forum aswell, or only stick with the blog?

Stick with a blog and do the normal Wordpress SEO stuff. Organic traffic is usually the best and easiest to maintain as long as your not going for any super competitive keyword

i agree with Rex

yep, start small. build up a loyal following to your blog and then look at adding a forum.

also, make use of social networking sites