Get some heavy cavalry and let them charge -> insta win.
At least it's like that for me.
You should go for higher tier targets exclusively like Lords, Miles or other knights. Charging into a group of archers is also a good idea, they will stop shooting at your men and try to hit you with their swords for a while.
Which weapons do you use? On the battlefield I use a lance to take down high priority targets fast and a two-handed cleaver-like sword (has around 50 swing damage) after the lance is broken. It's mostly a onehit for every enemy unit except knights and lords, they take two hits
Get a fast horse, I use a Heavy Palfrey, the one with 53 speed. Speed beats armor IMO, since you get higher speed bonuses on your attacks and you can outrun everything. Pick your targets wisely, the best way is to go for single soldiers, NEVER charge into a group of spearman or riders.
As for tactics, as I said, I let my soldiers charge (more than 50% riders though, when I muster my full army, otherwise 100% riders). If I get dismounted and I'm surrounded I press F1 then F2 which will cause everyone and his dog to run to my position. Very often very useful. Sometimes I will order my soliders to "Hold this position" if they are too far spread out and get mowed down by enemy cavalry or archers, but most times they do just fine.
Don't let the AI organize your tactics, while it may be a nice feature you will have way higher losses cause sometimes they will just stand there scratching their balls doing nothing while they get shot down by archers. This is especially true for cavalry, they are really best utilized if you just let them charge into the enemy. They will blast the enemy lines open and by the time your infantry arrives they can take them out in single combat.
Getting high quality troops really is paramount. Recruit all your lances from your fiefs and just go for low quality enemies like smaller lords and bandits, and skill your companion's trainer skills. After a few days they will be way better and you can disband them until the real deal begins. ATM I have around 30 nobles and 100 veterans in my village, same goes for my castle. You said you don't have issues with money so the wages shouldn't be a problem.
You should see to that your companions have halfway decent gear, if they are a onehit for enemy Pedes they just unnecessairy take up space in your army.