Each Inn provides different mercenaries for hire. If you find yourself with a little extra cash, and nothing to spend it on, build Inns.
RTFM. :) Especially pages 151 - 153. These pages contain the costs of structures and units. Note both the initial cost and the yearly upkeep. Make sure your economic base can afford both the upkeep and the building cost.
The cost of building a mine combined with it's yearly upkeep will be a drain on your initial resources. Wait a few months while you explore your surroundings to build the mine/factory/market combination. You may find a village close enough to link a factory/market. Remember, jobs and goods (if their resistance is < 50) lower an independent's resistance faster than spies and leadership.
Add a building strategy here.