I do not get how this SSL Certificate works. I have created a SSL certificate and key but I can not access my site through "https://". How do I use this feature?
Not really. SMF has converters for many different types of forum software. Although it kinda would be a waste of money to buy Invasion Power Board and then have to switch back.
Do you mean like PHP Web Programs such as Joomla (As CMS)?
CMS: Joomla 1.5
Forum: phpBB3 or myBB
Blog: WordPress
Course Management System (CMS as well): Moodle
If I were you, I would not be making my own forum. There are hundreds of them out there and I would not believe that you do not like any of them. If you actually successfully make one, I would like to try it out though
You can use different themes and everything should then be fine
If you would like to try other forums out, try going to http://www.opensourcecms.com and find a good software that fits your needs.