Not sure what agile teams you've worked with, but my agile teams have a delivery window predicted by the current backlog of work. If possible, don't define hard dates, define a delivery window based on confidence.

This is how people should be hired. Formally educated or self-taught is irrelevant. What matters is if you believe I can accomplish the work you need done within the time you expect. As a hiring manager, you either trust I can accomplish the job or you don't. My past experience can only really contribute to establishing (or harming) the trust in the potential business relationship. Ability to solve complex problems with clean engineering principles/practices is what should be sought out, not x number of years in a particular language or technology. After that you're negotiating a price that's hopefully within your budget to make a profit on my contributions.

I think much of game design boils down to balancing actions within the system rules. Teaching spreadsheets would be a good start. Take a look at the wiki on game balancing Lots of references for literature.