I think you should start by removing the docker idea as a variable because it’s just a layer of abstraction that can be added later. Its certainly possible for you to construct a docker container to do this, I just don’t think you’re at that stage.
What you should probably focus on first is getting an external Linux box talking to the TrueNAS using the API.
Using midclt externally shouldn’t be much different than using midclt locally. With the obvious exception of having to authenticate.
Happy to help bounce ideas here as you progress