Becky, Sam,
I'm sure you have great plans, and I'm grateful for all the wonderful things you have done so far. I also realise that running STCC/CTRA has cost you a lot of money, and that it will continue to be costly even with sponsoring.
Still, I'm against advertising. Not because of the bandwidth it costs; I have broadband, so I couldn't care less. But seeing ads does cost me money. Sponsors will only pay for the ads if they work. (OK, some sponsors may give money because they like your plans so much. But the average sponsor is well aware of the effectiveness of his ads.) Ads that work make sales rise, and the money from the sales came out of the pockets of the folks who watched the ads.
In short, the funds that you'd receive came from the visitors of your servers. But in an indirect way, and after the advertisement industry has gotten its share. You say you don't want to ask your visitors for money. But advertising also draws money from them -- without their consent, and (partly) outside their control.
With websites we've seen a technological arms race because of advertising. People who don't want to see ads invent ways to block them, and the folks who run the ads invent ways to circumvent the ad-blockers. Loads of effort has been spent in this war, in both camps. This may also happen in LFS.
Please consider this when you plan to cross the Rubicon.