1. I completely agree. We have recently acknowledged the power in an "alien" syntax as you put it. In v2.0.0 Odin will also support the classic cron schedule string syntax!
2. You are right, the repo is lacking a detailed description on this. The execution semantics boils down to at most once.
3. The Yaml file just lends some simple schedule and runtime info to the job. We actually would rather this moved into the code in v2.0.0 - that way all workflow info is self contained and no supplementary files are needed. The multiple data store thing is entirely an issue, in v.2.0.0 we are aiming to make more aspects (such as you have described) pluggable, using whatever data stores you specify. That will require a lot of docs but we are up to task.
That you so much for the advice comments, I will share them with the development team, feedback is always appreciated :)