I would figure out what is allowed by your ISP before going through any trouble. I am on Comcast (3.1Mb/256kb) in the U.S. and from what I understand, we are not supposed to even have a VPN setup? What a crock π
Anyway, unless you have a sick internet connection, especially with regards to upstream, you're not going to have much fun trying to offer service to anyone other than yourself.
As far as DNS, you can have any domain point at any IP, but if you are on cable, they probably use DHCP and that being the case you can't get a static IP out of them for any amount π
You could use a service like DynamicDNS but hosting sites for others without having a subnet is kind of a joke. Not that I am any authority on the matter but these are certainly considerations that must be made.
With that in mind, if I were still going forward with the endeavor, I would use Mandrake without a doubt!
For the sake of playing around, setup a gateway server with all the fixens, get that secure, and learn from there...
Build yourself an intranet.
Good luck