The fix you did for the redirect problem should work, but the only drawback to doing it that way is that your users will be redirected to your homepage anytime they log in. I guess that wouldn't be an issue in your case though since they have to be logged in to view the site.

You cookie settings do seem to be correct. You could try changing the Cookie Domain and just leave it blank. The .mysite.com seems to work best for most people, but in a few cases it seems to work better if it's left blank instead.
As for changing that template, just edit that template in your Admin CP. You should see the 2 links there, so just add /forums/ in front of the url to each of them.