It's possible, just a major unlikeness because of today's fixed perspective on towering. Many people believe towers are for hats rather than fun so they would much rather spam recruits to reach their goal faster. Yes, leading a single guild without any allies is possible but there would be a lack of motivation unless each of them is truly in it for the hat. You mentioned subguilding which is something Helsing has done, only recruiting other guild members and none other. It was hard enough doing that since whenever either someone with powers or whenever there was a low amount of people we basically had to suck it up and wait until more people got on and prayed we wouldn't get ambushes at that time. So again, yes 25 people is possible. But very, very unlikely.