Army Tactics - Close vs. Ranged.
Ranged units are solid choices against Bandit units but fall a little short against organized infantry with heavier armor and shields. Their range is typically countered by lighter armor and possibly no shield. Ranged units also can't do much against fast moving calvary.
Infantry units can be fodder for ranged units if not placed and moved correctly. I find that 'hiding' infantry behind a hill, and forcing enemy archers to close to short range works wonders. Using a "close" grouping (F
also helps keep your infantry alive as they're close together and can assist each other.
Calvary works VERY well against range, but can fall victim to pike/spear wielding foes. They also tend to run into a group of enemies and stay there, negating their mobility bonuses. Calvary are good when used in waves. "Charge!" (F3) will make them run out to engage, after they've gotten a few licks in, but before they get surrounded, order them to "Hold!" (F1) and return to where you are. This keeps them from being swarmed and dropped. Ranged Calvary is great, but sometimes runs in too close to a fight and gets mauled.
Arrows...
In sieges, you can try an scavenge arrows from fallen foes and friends. In regular combat, you have a footlocker at your starting point that you can open to swap around your inventory. Keep a few extra bags of arrows in there, and you'll never run dry. You can run around, fire at will, return and refill, then go back out for more.
Tactical Map...
A tactical map must might make medieval times too easy. You have to scout where the enemies are. One thing you can do, though, is watch where your troops are trying to charge to. Odds are, that's where the enemy is coming from.
Money...
Slavery is a great way to make cash. IMO, there ought to be some sort of renown penalty for it, though. Go from positive renown to negative and become infamous. It was pretty common practice back then, so I guess that's just today's standards. Another good way to make some solid coin is to enter tournaments at cities and bet on yourself. You've got to make it through 6 rounds of combat, sometimes solo, sometimes with an AI team, but you can get upwards of $4000. After you've won once in a city, the odds on you become less favorable, and you can walk away with less than $2000. Selling equipment also nets some good money, especially if you've got a good Trade skill. Sea Raiders and higher-end Deserters have the best neutral equipment that can be sold.
Troop Behavior...
Horse archers do tend to ride around, staying safe... but it's also harder to hit a target from horseback, so they might miss more often - I'd say it's a toss up, based mostly on what you want to do. Units will switch equipment based on the situation. Not every type of archer comes with a sword and shield. Some might just try to hit with their fists.
Heroes...
Heroes are great - They can learn skills you yourself might not want to spend points on (Check to see "Leader" vs. "Party" skills - Skills like Leadership only work for you, not them). Heroes also can't be killed; they can be knocked out, but not killed. Also, you can equip them however you want. The downside of heroes is that each has his/her own likes and dislikes - Some might have working with another hero or unit type, or they might detest certain activities. At any rate, based on your personal build, heroes can be a huge blessing - If you're a "lover, not a fighter" you could have superior fighting heroes that train your units. If you're a fighter first and foremost, your heroes could fill in gaps for Trade, Engineer, medical skills, Pathfinding, etc.
Allegiance...
You can remain 'neutral' as long as you want. Turning down offers to become a King's Vassal hurt your rep with the king, but not much else. Build up some Charisma and Leadership to increase your army capacity, or increase your renown - every 25 gives you +1 unit cap. Being a Merc or Vassal opens you up to unprovoked attack, but has benefits. You'll earn favor with the kingdom you side with, and as a vassal, you'll get to manage castles or lands for the King (if he likes you enough, he'll likely offer you a chance to manage newly captured lands). There's also the "Claimant" route, where you help a rejected King reclaim his 'rightful' throne, thus becoming his right-hand man. You can also try to conquer the whole map as a renegade, with no allegiance, but you're also soloing vs. everyone then.