While taking them to level 10 should be a long term plan, we should realize that the money spend on the expenditure for each level increase (roughly 2700 pounds per level) could be better spend elsewhere. Also 300 is the rough payback period per level....
Two areas of concern :
1) Capital formation : We will need to sustain our capital when its formed, with loans to encourage level1s from our other towns to come and become level2s in the capital. Since it wont be a colony, I have already started storing up bread, corn, meat, flour, wood, meat and a few other essentials for the capital
2) A more immediate concern is the new war code. We already were the first County to start a subsidized meat program. We already have a lot of high strength troops, which is great. Next on the priority list is equippage, and it is going to be expensive. Buying up the shields and swords would require a lot of initial capital.
Even at level 7, our overall mining system is very good mainly because we import the iron we need. So while long term, I support upgrading the mine to level 10, for the short term we have more immediate concerns. That said, we have ample reserves of iron and stone needed for any upgrades if the need arises.