Mr Frogboy provided some answers in PM. (Thank you!)
Main post updated.
Q: When you build on a mine inside an outpost, does it cost anything?
A. In the next update mines will cost 10 gold.
Q: What is intelligence good for? Does it have an affect on spell casters?
A. Intelligence helps your spell ability and your spell resistence.
Q: How is a unit's power rating calculated? And how is this value used if you use auto-resolve instead of playing out the tactical battle?
A. The combat rating of a unit is just a rough guide we use to get an approximation of a unit's non magical power. It isn't actually used. Auto-resolve simply plays a simplified version of tactical battles off screen.
Q: How does the existing initiative system work and how are "rounds" a part of this process? How can this info be viewed in the UI?
A. Initiatives are used to determine how often a unit gets a turn in battle. A unit with 20 initiative would get twice as many turns as a unit with 10 initiative.