I never knew that you have to sign contracts to take voice lessons. (Well how would I know, I never taken any lol) But if that is the case then yes. Don't sign anything. You must always have the freedom to leave the lessons if you feel you dont get the proper results, the lessons are not that good, or you just can't get along with your teacher. (hey it can happed lol)
I do agree with the choir not that good of a choice because you are too many. But what I had in mind was you join the choir, and try to get some solo time with the choir teacher to hear you sing. Get some thought from him then you can start practicing on your own. This is actually a cheap, and quite possibly free option if your keen on praticing alone.
But I can see your leaning more for the vocal lessons, and that is better.