Wow...what a diverse and amazing amount of feedback to my questions --
thank you.

As for the retraction settings concern, I'm pretty sure it isn't
related to plate leveling unless I really want to get super aggressive
with the z offset (dropping to under 0.1 from the current ~0.15) ---
I'm getting nearly perfect prints even with just 00.17 - .20 layer
height when I take the 20-30 minutes to do the leveling procedure as
described by rocketsled.  I haven't tried to go any lower than 0.17
layers - but the delay in restarting extrusion after travel in certain
cases always happens and is only really evident if one looks for it in
the floor of whatever object is being built.  I do have some minor
concerns about the smoothness of the HBP plate - it seems to be
slightly higher midway between all 4 screws and always highest in the
center. l should research what the max variance of the plate should
be.

I also haven't yet tried turning acceleration off.....I really like
the idea of slow changes to the extruder speed rather than having it
fixed and I've already reduced my default accel speed  to 60 for flow,
travel, and retract.  I'll have to do find a good test to see if my
filament diameter is set correctly...right now I'm setting it to the
max of several readings or avg filament reading + 0.03 whichever is
higher.  I may also need to do a test of what happens with retraction
distance is reduced to 0.

With regard to HBP temp, I'm going to test increasing to 112...but the
HBP temp seems to overshoot by up to 4 degrees when warming up and if
120 is the max limit, than perhaps 116 degrees would therefore be the
actual max safe value.  It isn't clear what other effects increasing
HBP temp might have, so I'll take baby steps first to 112 and then to
114 if still needed to prevent corner warping on long prints.

Another question did turn up over the last 48hrs and that is more a
question of the impact on the nozzle when one gets aggressive with z
offset and layer height and ones plate itself is not perfectly
smooth..I've seen a number of tiny flakes on the first layer and the
more aggressive I get, the dirtier I find the nozzle after each long
print.  I assume there is some kind of trade off between lifetime of
the nozzle and print detail.  At the moment, I'm sticking with 0.2
layer height and cleaning off the nozzle after each print while
retaining a z offset near 0.15.  I see several recommendations for z
offset of 0.1 or less but I worry that it is going to result in a very
short lived nozzle.

Matt