I did this section a long time ago ('99) but regularly ride on some of the PA and NJ portions so I can offer some detailed insight.
Norristown to New hope has some hills, but it's not particularly arduous. Anything really steep is short. There will be heavy traffic in places if you ride this section during a weekday. I strongly recommend doing it Sat. or Sun. and the earlier the better.
New Hope to Delaware Water Gap, PA is mostly flat to gently up hill as you go upstream along the Delaware River. There is one rather large hill above Milford, NJ and other smaller ones. There is also a long slog up SR 611 heading to Delaware Water Gap as you climb above the river. You should not encounter too much traffic in most areas. Phillipsburg might be one exception. Some of the road surfaces between Riegelsville, NJ and Phillipsburg, NJ may be chipped up a little. There is an option to ride a trail from Lambertville, NJ to around Milford. It's pleasant and easily rideable. I have done sections of it riding a road bike on 23c tires. I strongly recommend taking the trail at least as far north as Stockton, NJ as there is no shoulder on this stretch of SR NJ and it's windy in places. North of the north end of Stockton, SR 29 widens and has a wide shoulder until it ends in Frenchtown, NJ.
About 8 miles north of Lambertville you will pass Bull's Island Recreation Area. It's a fabulous place to camp. Ask for site 66 or 67 close to the river. Depending on the time of year, the place can be booked on the weekends (weekdays are mostly empty, except maybe during the time around Lambertville’s Shad Fest, and if you want to make a weekend reservation you must pay for two days unless you call Saturday morning and there is space available. If you are concerned, start off from Norristown on a Sunday and spend Sunday night there. The store in Stockton, NJ (in the old train station next to the trail) recently expanded their grocery selection. They also have some prepared foods and make sandwiches. Great wine and beer store in Stockton, too, just don’t let the park rangers catch you.
Worthington State Forest, across the river from Delaware Water Gap, PA, is another nice place to camp. (Skip Shady Acres in Portland, PA). Just note that the bear population in the Delaware Water Gap Nat’l Recreation Area has taken off over the years. The ride through the Gap is beautiful, but you will encounter some hills. North from Port Jervis, the road is a gentle up hill until you start a relatively short climb up to Otisville.
I don’t want to offer anymore detail since it’s been a while since I have been farther north, but I will says that I remember MA and CT being fairly hilly in places and that the U.S. 1 portions in ME were not that pleasant. Lots of noisy traffic.