I don't know if I'd say "most all" could be done in that amount of time, as the more you learn, the more you find there is to see & learn! However, I think a 5-day timeframe would allow you to hit the highlights with enough time to enjoy & absorb some of the things you learn there. Well worth it.
BTW, Boston is a tough town to drive in, and I would NOT do it in an RV. Camp outside the city (Normandy Farms in Foxboro is nice, and Minuteman CG near Lexington gets good reviews) and take the "T" (commuter rail) in. Tickets aren't expensive and you can get most anywhere in the city with them and a little walking. It's a great city to walk in!