You should check out GigPerformer by Deskew Technologies as an alternative to MainStage. Way better and more flexible, IMO. They gave their own scripting language, so you can go as far down the rabbit hole as you want to.
Regarding Open Stage, I’m mainly using it as a way to see both of my AbleSet machines running concurrently. You can also create custom buttons for OSC control like TouchOSC. See more here Ableset Workflow with Open Stage Control