In the beginning a relatively cheap mustketeer + pikemen/scythe army worked well for me. It is important to instruct the party well as described above: hold position, spread out/form 1 line, and fire as many muskets as possible, then melee only with the pikers/horsemen if you happen to have a few.
Later it became better to have a small, but strong cavalry. After level 7 I started to hunt tartar raiders and deserters. If the deserters have captives, you can hire them for your army at no cost - and you can have winged hussars and many advanced cavalry troops (dragoons, reiters, etc.)! Only their weekly cost is high. Now I have a team of cca. 45 men, all on horseback, +5 heroes, and I pay 700-800 talers for then every week. Most of the army is melee with poles, but I have Polish musketeers too (also mounted).
The advantage is they are very fast, you can chase any deserter or raider party (avg. map speed 6), and incredibly strong. No looters, bandits, deserters or raiders are dangerous to us, and great to protect caravans.
