I Mean essentially it would be the base game so how hard could it be.. it would all just take place in a sandbox-esk environment instead of played out through the whole campaign, maybe you could rob trains, houses, ect and re-use some things from campaign missions, maybe you could even get the missions from trelawny and have it play out "after the campaign" if you allow mp models
just a suggestion for another mod since i see you actually do a good job on scripts, maybe some type of sandbox mode(choose a mp model at start or just use john/arthru) where you rob houses, shops, stage coaches, people/maybe even do jobs like this one to earn legal money and take care of yourself/ gain notoriety.. kind of like rdrfr but the opposite side of the law 🙂