Adding law and trade bonuses to upper tier barracks doesn't seem like a good idea, you already have the city garrison buildings for the law bonus and the trade bonus doesn't feel right, although you could argue that at the highest level they'd produce more weapons than they need thus trade...
Be careful with placing mines, placing them near small factions in rebel settlements could work but don't give them to factions like Maks (be careful of the balance in Greece) doing something might make one of the factions there win in Greece all the time.
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