One thing that really annoyed me in the base game was the amount of time the slaves spent outside the mansion after level up requests. You could easily find half your slaves away on rotation all game long with grade increases and holidays. I fixed this in my own mod and it would be quite easy to put into other mods too.
In jobs&specs.gd, var leveluprequests, add a vacation requirement of 'person.metrics.ownership >= 7' and a slave won't ask for a holiday until they've been with you seven days. Add improvegrade requirement of person.level >= 4 and only the experienced slaves will be asking for a grade increase.