Hi Welcome to Sitepoint
I suppose the first question would be whether your time would be better spent on repairing PC's and setting up your business rather than learning the whole of webdesign on the fly - which can take years :).
It may be cheaper in the long run to hire someone to set this all up for you rather than trying to learn it from scratch.
I don't have any specific suggestions but you should be able to do all the things you want with a suitable CMS and you can find [some suggestions and [URL="http://www.smashingmagazine.com/2009/11/08/getting-started-with-content-management-systems/"]resources here](http://visionwidget.com/toolz/8-web-development/110-free-cms-resources.html).
You can uses services like [dropbox for uploading files and for offering advice and help you may be better of with a [URL="http://www.techsupportalert.com/best-free-website-forum-software.htm"]simple forum and indeed some CMSs will had [URL="http://www.bestofjoomla.com/content/blogsection/3/9/"]forum plugins](https://www.dropbox.com/) anyway.
Of course a suitable developer could tailor all these to your needs or indeed build something leaner from scratch.