My best advice for choson in RM is, play roman instead.
You get a better economy and scythed chariots, to go with your cheap towers and good legions.
If it really must be choson, avoid water maps. Build a network of towers covering each other going out from your town to stop CAs, then use cavs to kill any STs that will surely show up. Expand aggressively when you can. This may give you enough time to iron.
Towers should be in a triangle pattern like this:
===X===X===X===X===X==
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=X===X===X===X===X===X
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===X===X===X===X===X==
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=X===X===X===X===X===X
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===X===X===X===X===X==
Once in iron your priority should be HAs, long sword, iron shield, ballista towers, and legions. At this point use long swordsmen or legions to stop STs from hurting your towers, and HAs for attack.
Towering up an enemy base is very effective, but you must start far enough outside of their base so your towers cover each other before you're discovered. You also need axemen to counter slingers. Remember, you're not attacking their base, you're defending it (from it's own occupants).