First of all, there is no state agency that regulates statutory road associations, and you are not required to report to anyone. (We have had at least one person complain that there needs to be some sort of oversight or regulatory agency, but at this point there is not.) If you were set up as a non-profit, it would be a different story.
You mention your roads' "possible acceptance by the town as being town maintained." but then you say your association "will be dissolved when the town accepts the roads." Sorry to be the bearer of bad news, but I wouldn't count on it being accepted, even if you have assurance from a town official that it will be. Many towns, if not most towns, now have a policy of not accepting any new roads, or at least not accepting a road until it is brought up to full town road standard, which includes being paved. That can be prohibitively expensive for a small road association. Then once the road is brought up to standard, acceptance may require a vote of the townspeople, and if they think taking on maintenance of another road will raise their taxes they will likely vote against it. That's not saying it's impossible for it to be accepted, but I wouldn't count on it.
I agree with the other response in recommending the sample bylaws on the MARA Resources page. You can modify them to fit your specific road, but that will give you a good place to start. I would also highly recommend the MARA Conference on October 3rd as being a great introduction to the world of statutory road associations.
I believe the placement of stop signs would depend on the width of the road right-of-way as established in the subdivision plan. Usually the specified right of way includes a greater width than the driving surface, so as to allow for a shoulder and ditching. The subdivision plan should be available from your County Registry of Deeds. (Depending on what County you are in and how old the subdivision is, the plan may be available online. In any case, the Registrars may be able to help you find it.) As long as the sign is placed within the right of way bounds, you shouldn't have to ask permission. If you need to go beyond that, I would think you should get written permission from the landowner.
As for denying voting rights, the answer is no. For one thing, the current road association cannot enforce anything that happened before it existed. (The other members who did pay could possibly file in small claims court if they had to pay to make up the difference, but the road association itself can't collect a bill that was due before the association was formed.) But in addition to that, the statute requires that each parcel of land represents one vote. It would not be fair to deny a landowner his say in what is done with the road or with road association funds. Our country split from England due in part to the objection of taxation without representation! However, I can tell you from personal experience that if you do a good job with road maintenance under your new association, there's a good chance your non-paying member will begin making regular payments. My non-attorney advice would be to just figure you are starting with a clean slate.