I reiterate that I would save your money and not stay in the Back Bay area. Plus, I really prefer to board at South Station. Anything downtown or within walking distance from South Station will be fine at 8 pm at night.
Areas to avoid would mean that you would be on the T - and that in my opinion would include anything in places like Dorchester, Roxbury, or south of the Andrews T stop on the red line. you can go north on the red line all the way up to alewife and be perfectly in a safe neighborhood. I would avoid anything on the orange line to the west/south past Mass Ave (one stop after Back Bay, DEFINITELY avoid ruggles) and steer clear from anything on the Blue line.
You could stay on the silver line but I wouldn't go anywhere past where the Seaport hotel is into South Boston.
Durgin Park, in my opinion, is a tourist trap. If you want great Boston food, pay a visit to the boards at www.chowhound.com and get some recommendations. If you want seafood, you could try Legal Sea Foods or the Union Oyster House. For great steak, check out Moo (Beacon Hill) or KO Prime, which is at the Nine Zero. the Nine Zero is a beautiful and very modern hotel on Tremont Street which would be another good option for you.