Thanks for the answers so far, those gave some useful insights. I'm glad I am in no rush to get things going and can take the time to research my options properly.
Just to clarify, when I talked about donations I wasn't thinking about one off donations to the pool's expenses, but rather an optional percentage fee on the miner's earnings, unlocking some perks (such as mining on port 80 or something similar).
Kinlo, I also thought that the AGPL would require a MySQL module for Eloipool to be made available as source, so I'm wondering if nobody has actually written one or if those that have don't comply with the license. Anyway, if I end up writing one (alternatively I guess a flat file based approach could be more resource friendly...), I'll make sure it gets posted so that people can find it.
Wasn't aware that Slush's algorithm is hoppable - the impression I got from reading about the various methods was that it is specifically designed to prevent that. But it's quite possible that I missed something there. Do you happen to have any details?