the forum url : example.com/forum redirects to example.com/forum/ is this bad for SE's ?
It doesn't matter for SE's at all. Ideally it should always work that way (and it depends on the configuration of your server). If you enter minibb.com/forums for example, it will be redirected to minibb.com/forums/ - and it is correct.
I changed the text for the index.php file
The text you've changed won't be available on the page at all. And you can't remove it because it's part of the GPL license, i.e. your copyright agreement.
I saw my forum is indexed now but with the wrong description of threads
Description of threads should be build dynamically depending on the content of the first post.
Recently I've read the interesting point of view about SEO
and in many aspects support it. Study it carefully and you will be wondered that it's not important how
the pages are build, but what's