1) Yes. In systems.gdb you can change NewEventMinTime and NewEventMaxTime to slow down completely new stuff. You can also change MinEventTime and MaxEventTime in quests.gdb to change how fast specific quests cause more problems.
2) The NewEventMinTime and NewEventMaxTime change will affect the new recruits spawn rate.
3) You could try to change the MonsterChance type stuff in world.gdb in the AreaHome entry, but that might change the rarity of town attacking monsters also.
4) I'm not sure there is directly, but could probably change it's MinLevel to something like 200 so it was never available.
5) You want to change MaxSellPercent and MinSellPercent in systems.gdb.
Depths of Peril, Kivi's Underworld, Din's Curse, Drox Operative, Zombasite, Din's Legacy, & Drox Operative 2