The slave won't disappear from the game if you remove her image from the folders. Only the image of her will disappear. Which means that if you meet her at the auction there'll be a visual glitch (most probably a blue square with "?" in the middle).
Each numbered file in the json folder is a unique combination. There is a json file in the top level folder that contains the ranges for each age bracket. You could remove some JSON files, renumber the remaining ones so there are no missing numbers, and adjust the ranges to match.
Doesn't ring a bell but my first guess would be raising her level of obedience to max. Especially devotion to lvl 5.
There are some exception cases, but in general, have positive mood and max devotion, with arousal below max.
Yes. It's slow to reach the max level. And it can decrease from illness, drugs, etc.
Will eating S+ food and not being tired eventually get it or is the sex everyday and regular fighting also required?
The latter. Although you don't need to do it every day. It's an accumulation of progress over time.
They bind the first time you equip them. So, for convenience, you can buy a few sets at once when you have sparks to spare.
It is explained in the tutorial lectures. The development build (2.2.1) includes some improvements to the lectures.
