Depending on the rifle/projectile/purpose, I start between .0015" and .0030". With my AR rifles and other semi auto rifles, I lean more towards the .0030" side of things, and may also crimp. With lighter recoiling rifles such as my 13.5 lb .260 AI with a brake, I start around .0015". My braked 9lb .338 NM has right at .0020" neck tension. After some load development is complete, I may tweak the amount of neck sizing (I use a full length bushing die so I also bump the shoulder after about 3 fireings) to see if it helps accuracy/consistency of my load if I feel it is necessary, but those are my general starting points.
You drawing is correct in it's theory. I measure as previously stated, measure after sized, then again after the bullet is seated and subtract the difference.
Want to really confuse yourself? Start trying to figure out the correct amount of distance down the neck you should size with your bushing!!!