Having positions is good, even if only good practice for how things will be when you're incorporated. A chair should be a person who is organized and who can can lead meetings and keep them on track. A vice chair can step in to oversee meetings if the chair is missing. A secretary will be responsible for ensuring things like meeting transcripts are posted publicly, and ensuring that the board is in good communication with the community. Treasurer isn't needed till you have money, but again, it's good practice and you are going to need somebody eventually.
Not being professional or focused at this stage will only hurt the chapter in the long run. I suggest everybody take this stuff very seriously.
I'm not sure a vice chair is really necessary for such a small board. I would just decide that in the absence of the chair, the secretary chairs meetings, and in the absence of both, the treasurer does. In the absence of all 3, there is barely a quorum, so hopefully that won't happen too much, if it does the 2 people left can decide between themselves or just toss a coin - chairing a meeting of two people isn't a lot of work!