....
Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter whether
the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at least) is that
the finish that I did get with a nominally 'finishing' insert (larger
radius tip) was worse than with a smaller radius tip that is listed for
'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get a
single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it curls
down onto the cross-slide. Inevitably it falls forward towards the chuck
and if I don't stop the carriage feed (thereby breaking the chip) the
tangle of swarf gets caught up around the workpiece and mars the finish.

....
I bet your feed is too low for chipbreaking. My rule of thumb for carbide;
increase your speed, increase your feed. When I got trouble seems its always
one or the other. Find the vendors table for each individual insert, they
will show a box of feeds, DOC, and speeds for good results. For your
machine, these numbers are at the extreme top end of what the lathe can do.

On my 10EE, I use only CNMG inserts with the LF (light-fine) chipbreaker for
finish cuts. I often have trouble with the long stringys though. For
ruffing, I use a standard CNMG insert (any auction special), minimum 0.100"
DOC, .007" or more IPR feed, and then run the machine fast enough for the
chips to turn blue. 20 years ago, my instructor taught me: If your chips
aren't blue, you're going too slow. Your machine may not have the power and
rigidity to do this.

Personally, I'd strongly recommend that you use HSS almost exclusively on
this lathe. HSS excels at great finish and accurate cuts at the speeds and
feeds this lathe is made for. Brazed carbide bits might work well for you
also.

Karl