I suppose it depends on who hosts your site, as to how big a file they will let you upload. I used to be with cirtex, and had problems with anything bigger than about 7-8 meg. I'm with HostOnNet now, and have uploaded nearly 50Mb files. I've had some twitches, but they all play. As for getting your site full of videos and users, I'm afraid that is just normal site promotion. I'm lucky in that I have a ski forum which ticks over during the summer, then goes mad in the ski season. I'm adding videos as I go along, and encourage my visitors to do so as well. I make my own stuff, so there is a fair bit of originality, in a niche market, which helps.
Metacafe offer their users $5 for each thousand views, after approval of course, and after the video has been seen 20k times plus. Perhaps some sort of competition or reward to get users to your site?

HTH