Reading through your NIP I miss a narrative description of the flow you have in mind. It feels like at least 2 or 3 of these kind definitions are unnecessary. And it looks like you're thinking everybody will have all events from everybody at all times, which can't be true in Nostr.

You aren't considering what happens if an escrow agent vanishes, or to what relay each of these events should be published and in which relay each person should be reading from. The tasks are pretty undefined, you just give a string field to them, which makes me think if there is any point in standardizing the process at all, since all the work will have to be done manually and nothing can be automated maybe you can just do it with kind:1 notes written by humans -- honestly that would be a good idea, so after having some experience with that you can elaborate better on how to automate the flow and standardize on fields and events.