Bandwidth is a definite issue.....
We run the following tube sites:
http://www.jizzflixxx.com
http://www.pissflixxx.com
http://www.feetflixxx.com
http://www.gayfetishflixxx.com
All the sites are gay and do pretty well. We currently have 3 servers running the four sites and will be adding a fourth in a few weeks. I would say that the most important thing of running a tube site is the bandwidth and the servers. You will need to have the ability add servers on the fly. make sure your script allows you to add servers. If not, you could potentially have issues down the road. It's better to prepare in advance for the future than try to fix a problem when your already running full steam ahead. Our site jizzflixxx.com crashed a few times in the beginning due to lack of knowledge on our part. Once the users start coming in and the bandwidth gets sucked down there is no stopping it or putting it on hold. ;) So be prepared!!!
I do recommend using sponsor content as well as your own. The more the better. These sites grow fast!
If you have any questions do not hesitate to AIM or ICQ me. :) I'll gladly give you a helping hand....
:)