Just a suggestion that has worked well for some of my clients:
Go to the local permitting office and ask them to give you the names of several tradespersons in each category.
The recommendations from them will probably be the tradespersons who properly pull permits and do the quality of work that pass their inspections.
From that list, get written quotes and time frames from each tradesperson in each category.
Best of luck
My suggestion is to go back to the real estate agent that you purchased the property with. Usually they have a huge database of local contractors to tap into. Realtor are plugged into the local market well past just the sale or purchase of a home. If you do not have a relationship with a Cambridge agent it may be worth a phone call to get plugged into the local market.
If you cannot remember Angie's list is worth the membership rate and I would stay away from Craig's List as it can be questionable.
http://www.angieslist.com was the best $50 I spent (1 year membership). We have had met our share of crooks from craigslist - I can tell you that a bad contractor is worse than no work being done at all. So make sure whoever you hire knows what he is doing and has references. Btw, we had an incredible guy do structural work for us - had it not been for him, we would have probably had to go bankrupt. His name is Jeffrey Spiby and his phone number is 508-454-7627. He is very very reasonable and really knows his stuff (he is also on craigslist).
Angies list does require membership with a fee involved.
Best of luck