My recommendation would be to go with a Statutory Road Association under 23 MRSA 3101-3104, which can be done fairly easily by just following the law to the letter. You need to hire a Notary for the initial filing, but no attorney is required. If you need any help along the way, there are a number of us here on the forum who can help, and the Resources page provides manuals and sample forms. But I have to admit I am not familiar with the process for a non-profit road association, and I don't know what advantage there is in going that route. I do know that a statutory road association has the advantages of not being required to file annually with the state, as well as having the framework and the enforcement tools provided in the statutes.
If you do decide you need an attorney, Mary Denison would be my first thought too. However, someone else commented recently that they had tried her but she was not taking on new clients at the moment. If you contact her, I'd suggest asking IF she can take you on, and if not, if she can recommend someone else. I remember telling her a couple of years ago that I didn't know of any other attorney that knows road association law like she does, and she looked surprised and rattled off the names of some others.
I would give John Cunningham of Eaton Peabody equally high praise. I've always known him as top of the line when it comes to abandoned and discontinued roads, but at last fall's MARA conference I came to appreciate his expertise re: road associations as well. I really liked his comment that he sees his job as keeping you out of court by making sure your association is set up in a way that cannot be challenged.
That being said, the advice of both attorneys at the conference largely boiled down to making sure you follow the law to the letter. If you do that, you should be fine. If you're not comfortable with that, I'd suggest getting everything as ready as you can on your own, run it past someone with a successful statutory road association, and maybe then have a brief consultation with an experienced road association attorney just to make sure it's all in order.