Ok, I think the real problem here is that you have a committee (the board) making decisions but that you are not all in the same room so that issues can be brought up, discussed and decided all at once. And if this dynamic is ever going to change then one of two things needs to happen. Either you set up a regular meeting time to discuss any and all issues and whoever shows up to the meeting gets to vote (meeting doesn't have to be in person, it can be via conference call or chat room) OR you elect one person to serve as president (or similar title) who then takes charge to field suggestions, get feedback and make a decision.
In the case of the flyer, when he didn't reply right away to your "when can you have that done?" inquiry, then you might have replied that if you didn't hear back from him or anyone else volunteering to handle it by a certain time/date, it would default back to the original flyer. (20/20 hindsight at work here, but for next time...)
In the case of adding new members, since you are the one who would have to do the work, I think it's absolutely OK to say right out, I cannot commit to doing the work it will take to add new members. Unless someone can commit by time/date to doing that work, then unfortunately it won't be possible to add new members at this time.
It seems to me that you are not asserting yourself because maybe you don't want to appear to be pushy or appear to be making decisions without the authorization to do so. But sometimes, that's just what needs to happen, at least for now, the way the group is set up.
Once you get beyond this issue, or at least for next year when you go through initilal organization again, I think you need to implement a better way to handle issues and decisions.