As far as the 1.2 tip goes - it was not through any real planning - it was just the one that was on the gun!
But it seemed to work OK.
And as for water traps....er....I didn't use one. I know that's wrong, and maybe I was just lucky as I didn't get any drips through the gun. That said, I would use one as insurance when I do another car.

And as for painting half the car at a time - you've gotta do what you've gotta do! With a satin finish it'll be more forgiving when you get overspray (as you will when you do the horizontal parts), but you just have to deal with what happens when it happens! Again - don't let it put you off.
I have no idea why, but I definitely didn't get as much airborne paint dust with the Tremclad as I have in the past with single stage urethanes.
The tip about moving the compressor outside is a good one - if your neighbors don't mind the noise!

And as for the 50' hose - it's worth it for sure, but they're a pain to roll up afterwards, and watch for kinks!!