Bows vs Crossbows: Without sufficient power shot (i.e. lower level troops), bows just don't do as much damage per-shot as crossbows. And because armor/ironskin (ironskin only works in Warband) reduces damage per-shot, bow users below the top tier will often do little or no damage per shot.
Vassals: In some versions, you can only win by having all lords in your faction. So ultimately, you'll want as many as you can get, even the irritable ones. Fight alongside them then talk about it and throw banquets, and ask a lady to improve your opinion with any lord you have a negative opinion with (because honestly, just paying gold is far easier than those other two methods). Most guides I've read recommend building a couple superlords and keeping everyone else at one holding. Regardless of your policy of handing out holdings, the facts that you generally need one holding per lord and you want as many lords as possible will mean that distribution of holdings is a rather irregular way of getting lords to like you.
Tip: The best way to get lords in all factions to like you is to do the various claimant quests, provided you're able to complete them. You'll want 4 in persuasion, the ability to field an army of around 40 soldiers, and solid field combat skills (sieges are a meatgrinder: just bring a bow/crossbow and shield and carefully pick off enemy troops while your men do the real fighting). Optionally, you'll want to obtain a castle/city each time in the claimant's faction, target factions currently losing wars (smaller factions mean smaller domain that you need to conquer in order to finish), a force of huskarls/master crossbowmen for sieges, and a strong cavalry force for the field. Personally, I like either myself or a companion to have a decent level (20 or so) along with training skill. So basically, you use your power to determine holding owners to win friends throughout the claimant quest, then surrender your holdings so you can repeat with another faction. Not really sure how much better it is than just doing quests for nobles prior to joining their faction (once you join their faction, the quests get harder, better to play postman multiple times than get bogged down with a "capture specific prisoners" quest).
Horsies: The key to a cavalry force is critical mass. One or two mounted units: Fodder. Twenty or thirty horsemen: Slaughtering maelstrom. The quality of the horses don't matter as much as the quantity, hence why Khergit are better if you're trying to create a mounted force early on, as they get guaranteed horses at tier 2 and random at tier 1. And yes, the AI can suck at using horses. Best to use the follow command periodically to keep your horses from dying. For what it's worth, the AI is equally bad at managing Rhodok/Nord Shieldwall tactics. Sometimes, the AI gets lucky, but usually it just charges and the infantry die piecemeal.
If you really want to see better AI, try Pendor and some of the other mods. They have an improved AI that actually forms shield walls, skirmishes with horse archers, and swipes the flanks with horsemen.