You don't need to cool an entire house unless you have a family or pets and even still you can get away with using a 24" pedestal fan with using the AC you can cool an additional 900 sq ft on top of what the ac is providing in the living room.

I mean yeah a mini split is the modern option but not everyone wants to drill into their homes.

It's all about needs vs generalizations. I don't need to cool every room in my house and I can get away with using one whirlpool brand window ac in my living room and sending the cool air through my house with a penguin pedestal fan from Ocean State job lot.

Yeah it sucks having to put it in the window every year and it sucks bringing the fan down and walking by it but I have a natgas boiler based steam radiator system with heat in every room and given how the winters in New England are harsher than the summers, I think I'm okay.

and how many to cool a house and how much power does each draw.

Based on power consumption and practicality:

Well obviously it would take more a.c.'s to cool a house but again it depends on needs. If the house was a single floor unit it wouldn't need a mini split. It could use a window a.c. which can be 120v; mini splits are 220v-240v. It's probably a little more on volts but that's if both are ran at the same time. If you're in a main room while the main bed room AC is off you're not consuming twice as much power.

But the more cassettes with mini splits the more power you draw, the more you have them on the more energy you're consuming regardless.

So if you have two cassettes running 4 units, you're running 2 zones per cassette at 220v-240v each cassette plus the refrigerant, plus the amount of time on which can get to over 1,000w each easily. How they make it cost effective, idk. Maybe city programs but they cost 4 times as much as my window ac, the unit not the amount of money to run them.

I'm only going to use my AC 4 months out of the year, if that. It doesn't seem worth drilling into my house for 4 months out of the year.

In my honest opinion, I believe you can lower power consumption by not using an ac as much and by not having as many but you gotta do it right based on living needs otherwise you're gonna have a heat stroke.