Likely you already have a system for auto questing in mind, but let me throw in an idea.
Variable:
- each quest gets a priority (unsigned int), multiple quests can have the same priority.
- default value is 0 (if you need an disabled flag use 0 for that and 1 as default)
Hero becomes idle:
-> list the quests with the highest priority and sort them by needed heroes (your choice which one should be preferred)
-> start the first one possible
-> Still idle heroes?
-> list quests that can be done by all idle heroes and sort them by priority
-> start the first one that has needs less time than the shortest ongoing mission has remaining
-> if none meets the criteria leave the hero idle
The config menu:
- list all quests by priority first and name second
- display the priority of each quests as number
- let the user increase/decrease the priority over two arrows (per quest)
- (quests could jump in the list because the first sort parameter is changed and the second ignored)
Is there a reason for the sub-optimal auto questing?
When it has to choose a repeatable Quest it will cycle through all of them instead of focusing some that are objectively better. For example Guard Duty (200EXP in 80 sec for me) will have to wait a whole cycle of minor quests (50EXP in 60 sec).
 "Dragon of Ecology"){kind=icon}
 "Mental Incremental"){kind=icon}
 "Groundhog Life"){kind=icon}
 "Demon War: Idle Rebellion"){kind=icon}
 "Five amigos IDLE"){kind=icon}
 "The Perfect Tower"){kind=icon}
 "Spell idle 2"){kind=icon}
 "Increment RPG"){kind=icon}
 "The New Idle Blacksmith"){kind=icon}
Thank you for using "Game bug" button. I'm Working on #Reborn update, this bug will be fixed too. :)