I have 175/65 R15 tyres on steel wheels. Wheel dimension is 5.5J x 15, hole spacing is 4 x 100, centre hole is 56mm. Here in Switzerland it's recommended the tyres are not older than 6 years and profile not less than 4 mm.
If buying used the owner should be able to provide these details, the age is written on the tyre wall with a DOT number which shows week and year of production E.g. 3812. I have Semperit speed grip 2 tyres and would recommend not going for the cheapest make as they can have a bad performance.
The original mini one wheels should also fit and make sure the wheels are balanced as well.
Basically don't try to save money at the cost of safety!