This challenge requires no expansion packs, though Ambitions certainly helps, for selecting self-employed as a career.

1) Build a family of 1-6 people, and set them on a rural plot, which means give them a home, but leave plenty of room for croplands and a barn.
2) Make a small, very basic living space in the loft of the barn. Include the cheapest single or double bed, a bookcase and some chairs, maybe even a stereo if you're feeling nice. Build an outhouse and a rustic shower shack near or inside the barn.
3) Get the farm started. Even the owners should know a thing or two about raising crops, so get them to work in the fields! In just a few days, you'll probably have the basic plants, like tomato or lettuce, yielding harvests. You should maintain AT LEAST twenty-five plants on your lot prior to introducing farmhands.
4) NOW make yourself a pair of farmhands. Could be a married couple, could be buddies, it's entirely up to you! I would suggest giving them traits like "Loves the Outdoors" or "Green Thumb", but you can be as benevolent or as cruel a god as you like. <insert evil cackle> Then, merge them with the household.
5) If you're playing without expansion packs, you'll probably need to get the adult members of the household part time jobs, since if you change active households the game will likely assign them a career. If you happen to get exp packs (namely Ambitions) later, you can do away with this step and just have them register as self-employed at City Hall.
6) Socialization is entirely up to you. I prefer to initiate only mean commands when the family interacts with the farmhands, but you can mix it up. Maybe the farmer's daughter has a heart of gold.. maybe the farmer's wife is a little lonely. Or maybe they're all horribly mean. Let your creativity go with it!
7) Finances: here's where it gets tricky. You can sell fruits and vegetables at the supermarket, and the nice thing is that when you click on the building, it tells you how much your goods are worth (provided you keep the inventory in one sim only, but you can easily keep a calculator handy if you don't want the trouble of shifting crops around). Every Saturday is farmer's market. Have your sims sell as much as you think is expendable for profit, considering that the farmhands likely eat the crops for nourishment, and the household needs to pay the bills, make renovations, etc. Calculate the total sold, and then purchase an item worth HALF of that. Stick it someplace it can't be used: a storage shed without doors, for example. Just stick it in there and let it rust.
8) This stockpile of items is the farmhands' trust fund. You have a choice of two objectives. Keeping in mind that items devalue after they are purchased (consider it interest, wink wink), you can either earn 20K worth of items, sell them, and this frees the farmhands to move out and find a place of their own, get real jobs, etc.. OR! You can save to 100K and kick the family out, allowing the farmhands to take over the business! I guess it all depends on who you end up favoring.
9) A couple spare rules I tend to consider: a farmhand cannot get pregnant *intentionally* prior to at least 20K earned. This means that if you switch active households and she magically gets knocked up, oh well. You'll just have to figure that one out yourself!
10) The farmhands cannot be directed into the house for anything: using the toilet, showering, eating with the family, etc. UNLESS there's a party going on.
11) No perfect garden lifetime wishes. You should want the farmhands to escape their lives of servitude so they can do what they REALLY want to do, even if they happen to enjoy gardening just a bit.
12) Don't use works of art in your stockpile! Items must devalue over time, not increase in value! The only exception is if you happen to bless the farmhands' living space with an easel. The paintings they create can be used in the stockpile.
13) The farmhands' living space can never be upgraded in any way! If the stereo dies, find someone in the household to repair it. If it's beyond repair, oh well. That 20K just looks all the sweeter, doesn't it? The outhouse and shower stall, should they go completely kaput, CAN be replaced, but not upgraded in any way.
14) No classes or paid entertainment for the farmhands. Don't even bother with those aspiration rewards that give you free dining or theater tickets.. Bonus points if you can resist using ANY of the farmhands' lifetime aspiration points until after your goal's been met!

Enjoy!

I want to start a medieval neighborhood and I think, this challenge is perfect for this gameplay.

i like this one a lot! i think i'm going to start it soon.