After playing with the settings a bit, I've determined that the optimum size for these bad boys is an inch square. And NOW I get into legalities. Most icons are fandom-related, made from copyrighted images. Using them for LJ is toeing a fine enough line, legally, although I think the argument can be made that this is "fair use." Making a profit on them, however, is a whole 'nother biscuit.
So, I probably can't "sell" them as such. But...taking donations to cover cost of materials? That should be kosher, shouldn't it?