1. Go buy yourself a blunt weapon and go hunting for looters south of Tihr. Should have 3~5 looters spawning there constantly. Nab a bunch of prisoners than sell it to Ramun at Tihr for 50 a pop. With starting 3 leadership you can carry 40 prisoners. 40x50 = 2000 easy money. It's ALOT easier with Zerrinikian since harvesters/reapers are equipped with a blunt weapon and can make things faster. In one in game week I can make 15k. Subtract the 700 for upkeep and thats 14.3k profit every ingame week. Keep doing this til you get 100k. Also this will increase your weapon profieciencies real quick. Looters have no armor so you do more damage per hit which means quicker increases.
2. Pay attention to the world map and wait til someone captures a castle (usually near Swadian territory). I prefer Grunwalder since it's real easy to defend with archers. Also make sure the village that's attached to it has a high population so you can garrison troops. This point on get rid of any mercenaries you have (overpriced) and start replacing it with your homeland troops. If you still don't have a barracks go around recruiting peasants from villages and if you have a NPC with a decent training skill they'll go to Peasant+ real quick just by resting in the castle.
3. If you have to funds go and make peace with whatever faction you took the castle from. Usually is only like 3k. Get a barracks real fast. After that just start garrisoning troops in your castle. Do upgrades to your castle and let time go by to lower your badboy rating. Now with a badboy rating of 0, you won't have to worry about factions attacking your castle. Now go build up money again (quests for mercs, trading fur, selling looters) til you hit 100k again. Hopefully by now you'll be walking with a 100 size party and 150 troops in your castle.
4. If you picked a castle near the middle, chances are castles near you are constantly swapping hands. This time go do the same thing and capture it when someone takes it. Go pay the money to make peace with whatever faction. Recruit a lord and give him the castle. He doesn't need the village right now since you're at peace with everyone. Build up moneys again and repeat. With 3 castles/villages, you should have 3 lords. Give them a castle/village. Than go siege a town. Take the town and congrats you're on your own from there since that's where I'm at.
BTW this way is easy but it takes incredibly long. I'm at day 284 right now with 3 castles and one town.