I wouldn’t be upset if we went with Yotsuba. I love manga and I hear Yotsuba is incredibly cute. Since I already love manga (I read a lot of manga but I’ve only read english translations so far), I think it’d be cool if my first book I read in Japanese (from cover to cover, anyway) is a manga. Plus, since everyone says Yotsuba is so simple, I would probably be able to have time to participate while still studying Genki like I want to. So if we go with Yotsuba as the first book, I’ll start participating now instead of waiting until next year. 
Though, I do also want to read “actual” books so I would want to go with something other than manga for our second book.
Whatever we decide to go with, I hope someone will post some links of good places to purchase from?