I'd actually suggest making a single sim, buying the cheapest apartment in San Myshuno, delete everything (bulldoze) INCLUDING walls, then using cheats to remove your money (testingcheats true > money 0 > testingcheats false). You can unfold it however you want, I'd suggest trying to get a bite of the city life, as it can drain some cash in the start. As a fun extra challenge, get your sim pregnant instantly, forcing you to get enough money in 3-5 days to take care of a little one.
If you like playing with mods, I'd suggest mods such as Higher Bills mod, MCCC (Good for story progression) & some I can't remember the name of, that forces you into buying stuffs ingredients first, making simple meals much more expensive.
Also, a legacy challenge based on serial romantics (aspiration not necessary)
Basically, you'll need female heirs or males who can get pregnant/get abducted by aliens. The rules I play with, are quite simple:
- Your sim must never marry another sim.
- Your sim cannot move other sims in
- Your sim can't have several children with the same man (unless twins/triplets obv.)
Basically, you have to raise every simoleon by yourself. I tried myself with having the first child (who became heir) very early, I was lucky that the budget covered for even a tiny room and some toys when she became a toddler.
You could also make a blog or something - some stories and alike. That's fun to make, and people enjoy reading it and seeing pictures from your sims' lives.
Happy simming!