1. What's the practical difference between a 900/1200 pound pressure plate?

A stiffer feeling clutch. Probably no difference in life.

2. Do you bother replacing non torque-to-yield pressure plate bolts?

I would do it. I'd replace the throwout bearing and anything else in
the bell end that looks the slightest bit worn. Better to change it now
while you have it apart than have to change it later when it's not. My
inclination is also to clean everything out with naptha and to repack the
new bearing with mobil 1 grease.

3. Do you change the teeth spacing in your flywheel? Why?

You would do that if you wanted to use a different starter. Maybe the starter
for your model is discontinued. Maybe you have a box of cheap starters with
slightly different teeth. I have had to do it before when I could not get a
starter with the correct bendix.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."