Trip report coming soon.  Saw maybe 7 moose.  To answer my own questions:

1. If I finish the days paddling by 2pm, how available will campsites be?

A campsite was normally available in the area.  Some campsites have multiple "cells" meaning
two groups camping in the same area sharing an outhouse (instead of thunder boxes, they have actual outhouses).

2. How safe is the water compared to Quetico water?

By all reports, not as safe but there are particular places where you can access springs or water at a ranger station.

3. If on my first day, I put in on Chamberlain lake at 10am, how likely is it I will be wound-bound?

We put in around noon and faced a stiff head wind but were not windbound.  But evidently being windbound is not uncommon.

4. What is camping by Allagash Falls like?  Is it a crowded zoo?  Is it a scenic area worth the crowds, if any?

We liked camping there.  There are 4 "cells" for camping, so you are near a portage trail and it is like camping in a national forest campground with another group nearby.  But it had the advantage of breaking up the half-mile portage and gave plenty of time to enjoy the falls.

5. Any particular campsites to recommend for or against?

All the sites we stopped at were pretty good.  Quality is much more consistent than the quality of Quetico campsites.