There are three things you need to have in order to mod dominions. A text editor, the modding .pdf in your dominions/docs folder, and edi's database. The last isn't strictly necessary, but should be considered as a must for anyone who wants to do modding, because it will make your life much easier. A text editor can be something as simple as notepad.
All your stated goals are attainable, aside from the mention of causing militia to not count for routing purposes. That's just not built into the game, so I'm afraid it's not really doable.
Various suggestions for improving militia: change them to the shielded militia instead of unshielded, change them to light infantry, make them cost even less, turn them into yet some other unit, or just improve the equipment they wear a bit in some other fashion. By the way, it's probably better to use small groups of them as cannon fodder in each battle, retaining the rest on 'guard commander' orders. This way they can serve the purpose of dying for the greater good, while not counting significantly towards routing purposes.
And if you really want to improve markata (gasp!), I suggest using the markata madness mod! I assure you that this is the best and most balanced mod ever made attempting to balance the dreaded markata. Link here
http://forum.shrapnelgames.com/showthread.php?t=44771