About when it changes up and down gear when in drive, that depends on how the box works, some are better and more complex than others, and some are more sporty than others.
Some of them (when in sport mode) will kick down at the lightest bit of throttle and rev all the way to the limiter in each gear, giving max performance, so take a bit more encouragment.

Most cars if you in 1-2-3 etc and hit the top of the revs, you just bounce off the limiter like a normal car.
Tho ive driven some gay cars when it changes up, spoiling your fun.

Dont need to let off to change gear in a auto mate, full throttle shifts all the way!

The rpm thing on the stall converter is what revs the converter locks up and the car drives from.
Basically as standard most cars will drive (ie the converter locks up, like the clutch being lifted) from pretty much 1000rpm, which isnt exactly good for launching hard when you launching at idle!
So you buy a torque converter for the sort of rpm you wanna launch at, job done.

PS- Im still learining too tho, but gonna run an auto with the turbo v8, stall converter high enough so it launches on boost, and a manual valve body so i do the gearchanges myself.
Really looking forward to it TBH!

PPS- Jegs, good call, cheap as fook, ill be buying the Demon Blow Thru from there i think.