Not sure about the last post stuff, probably a bug with the importer. If you make a post in those forums (then delete it) you should be ok.
Yes, to limit the stylesheets people can use, simply uncheck them. Then the users won't even see it as an option.
The copyright notice isn't modifiable, as it voilates the license agreement to remove it. So not sure what you were looking to do there.
But both that and the contact us link can be found in the ubbt_footer.tmpl template file. <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" /> You can remove the contact us link, or change it to a different link if you wish.
