Crushs open world concept will be different than traditional sandbox games. It will just be optional missions/choices/paths, whatever you want to call it. Basically the game becomes non-linear or has short branching side quests (though the sidequests themselves would all be pretty linear). Non linear implies those paths continue to the end, but no they would really be side quests that do end and affect the MCs stats. Whereas there will also exist non-linear main story paths for different endings possibly but unlikely until the game is completed.
So these side quests will basically be events that happen on the side, from sleeping with clients to espionage missions, etc. You don't need a map to do this, and part of the sandbox part would be you get to buy/design your own wardrobe. But mainly you can just present different options on the screen to start missions... either in the MCs hostel or at her bar job or at the safe house via her laptop/phone or in conversation with her support team.
Perhaps later on failing to do/complete certain side missions a certain way will affect the ending of the main story as well.
I'm pretty sure crush could write like up to 10 side quests and have them completed in the same time frame it takes him to do updates currently, depending on how long they are. He would be better off outsourcing some of these side quests to other writers/volunteers who write them... and then just editing them for style and content and putting them together, since this will save him time... but it also depends how well those writers can write.
but yeah i could see this game having 50+ quests within a year? again depending on how long they are, some would be short, some medium, some really long. potentially side quests could be things that continually get added to the game even after the game is finished. so there would eventually be a lot. once there is a good base number crush would continue with the main story. probably before sidequests he would bring back the life path and start using the character sheet since sidequests would also affect the character sheet?
sidequests would be linear mini stories though... perhaps branching them slightly in places would be possible, but it would be like designing 2 side quests and would take additional time, so i can't see this happening unless it was just 1 scene at the end that changes depending your choices throughout the whole side quest. and yeah many of these sidequests would be about kinks/sex with clients, maybe humiltation kink, or exhibitionism, or gangbangs etc. and there is some sort of mission involved with the client, potentially or the sex with client is some way to build trust within the organization she's trying infiltrate. maybe it's the only way to get that client to invite the MC to a party that she needs to attend in the main story line. or perhaps she needs to collect info on how all these special VIP clients operate/fit into the crime organization shes investigating. it's optional to get some of this intel etc. but maybe the intel helps her later in the main quest with dialogue choices or in her espionage mission because she knows what to expect. like camera placements because she had a gangbang in that place rofl.