I normally just lurk, but I have just paddled NFCT Section 3, and I seriously don't recommend it. It didn't end my trip, but it has necessitated a delay while I heal from accumulated injuries and do some (minor) repair work on the canoe.
I did do it in a WC canoe, which I don't think is as bad a choice as many would think, although mine was built to deal with rocks and has half ribs which in my experience make a huge difference in the ability of a WC canoe to take punishment. A royalex or similar heavy canoe would be great for the rapids but pretty difficult on the portages, especially if it's longer. I had to do 3 pt turns with a 13' canoe on a couple carries, and some of the carries are pretty much straight up. On the river a kevlar or light WC canoe would probably not take the pounding and dragging. The best canoe for this trip would, however, probably be someone else's canoe.
The scenery is so-so. There are some pretty sections if you like marshy places, but they are connected by some nasty water. The camping is difficult as there are limited official places to camp once you leave Union Falls Pond. Early in the season you might find some stealth-y places to camp, but by July this probably isn't likely. Camping in a legitimate location requires doing two very long days on tough water for the last two days of the trip.
The water when I did it (early June) was already "too low to run", and my initial plan was to shuttle around all this. I allowed myself to be talked out of this, which was a bad move, and I had quite a bit of trouble with low water. I ended up getting part of me and half the canoe swept under a large log that was caught on a bridge abutment when I wasn't quite able to make it across the river in time. That was a few seconds of so many scary things happening at one time I would be hard put to list them all. But I was very lucky; the canoe did not broach although it came close and I was able to get it turned at the last minute so it went under the log parallel to the current. Once I unstuck myself, I was able to sink the canoe enough to pass it under the log and get it into an eddy where I could bail. I hurt myself later when I was wading (couldn't line from shore) across a series of slippery ledges that mostly didn't even have enough water to float the canoe.
I also got lots of stories from people in the days leading up to this about being really careful around Plattsburgh, as a number of people had stolen gear stories to tell. I had no issues with this, because there weren't many people around and most would carefully avoid looking at me (I guess I looked weird?!). I also met a number of really helpful nice people, so I imagine Plattsburgh is like anywhere else. There are a number of road portages in section 3, and at best they are at least quick to roll if you have a cart, and at worst require dealing with a number of loose aggressive dogs (no owners in sight). With all low water issues I had, I grew to dread the road portages the most because I was never quite sure if I would make it to the other end in one piece. A couple of big guys might not have this issue, though.
In closing, I agree with the folks who point out that there are much better places to paddle in the Adks and vicinity. If you want to do this section, I would do it earlier in the spring when there is more water in the river. July is way too late unless it's post-hurricane or something like that.