i think seo does not depent on your cms. you can start making on-site seo to your forum. it will a good start for you
i suggest you to find backlinks for your site. the answer of your question depennts on the power of your backlinks
i think http://forums.digitalpoint.com/showthread.php?t=315153 is great start point for you and i also suggest you to look the sticky threads on dp link development forums
You can build backlinks by asking for reviews from the bloggers on your forums or writing articles based on your forum niche
This is really a good one. Plus also see that you have SEO optimized URL's and if you don't have mod_rewrite mod for the forum software you are using then check that it doesn't have too many arguments in the query string. Thanks.
It depends on the forum software, but generally speaking there's alot you can do. Create keyword rich forum descriptions, block junk files/folders with robots.txt so you don't blow your crawl budget, rewrite URL's etc.
I am with sweetfunny. It depend on the forum portal that you are using. Search engine friendly url must be turn on. You can do this using pre-made plugin or mod rewrite in .htaccess. Try to get backlinks from related sites ( prefer have pr 5 and above ) and google bots will never leave your forum.