Also coming from Boston area, we found the ICW trip really wonderful. Much prettier than expected. Not very crowded. Lots of good stops. To you question:
Be conservative on miles. 50 miles is a pretty good day - especially in the fall when it is getting dark just after 4PM. When we can, we plan a leisurely 100 miles in three days with two days of 50 miles and one day off for sightseeing, maintenance, weather, or just to not hear the engine. Also we always break up the trip by leaving the boat halfway for three-four weeks in a marina and flying home. Or simply stop for two weeks and really explore a place like Charleston.
Don't get started too late. The first winter gales can hit the NJ coast in early October making it hard to get out of New England. And November can be uncomfortably cold in the Chesapeake. If you want to have really comfortable days in the cockpit and not wish for a heater at night try to get to Norfolk by October 1 and Charleston by November 1. Also, try to have an insurance policy with a hurricane box that lets you go south early. Many don't let you go south of Norfolk until November 1 but others let you go all the way to the Florida border by that date.
We (and most people we know doing the ICW) use ActiveCaptain. Sure it has some inaccurate postings, but if there are 20 postings about a shallow spot, we take it slow. We also use ActiveCaptain with Garmin Blue Chart on an Ipad. The person steering uses the chartplotter. The other person looks a few miles ahead on the Ipad for shallow areas, etc. A great way to share the navigation load.
You will meet a lot of people who will become friends. Another reason to not be in too much of a hurry. Print up some "boat cards" with your boat name, your names, and an email address. Keep a list somewhere about people you meet. If you do the trip more than once, you'll see them again.