1. A battle sizer mod , or the battle size option ingame might help you out.
Also the tactic skill lets you deploy more troops in comparison to your foe
2. Maybe he got captured? Happens some times. But you must be really unlucky
3. Its always a good idea to do the trading before you start a campaign(of war) or align yourself with some faction, so you dont have to rely on trade for that matter.
When you play as a trader, you can avoid war easily. No one except the bandits will bother you.
Pro Tip

Get some cash thru trade, quests, bandits
Get your companions, some decent equipment
Skill primarily charisma (leadership! ) and out source party skills (tracking, doctor, trade) to your companions
Build just a small army for starters, quality instead of quantity. horseman when you want to travel fast.
When you feel ready, swear your fealty