Depending on the size of your place, a decent stereo amp (Sony, Yamaha, Pioneer, Denon, Marantz, etc) from the late 80s-late 90s offering up around 2x100W into 6/8 ohms, and a pair of Mordaunt Short, Mission, Wharfedale, Celestion or Tannoy speakers of equivalent rating will be perfect unless your place is literally MASSIVE.
Even if you’re young and are having a “Skins”-type party where there’s like 150 people in a 4 bedroom house, then they’ll probably enjoy it more than a night at a local club lol. One thing I WILL say, however, is unless you’ve got a pair of “proper” floorstanders (at least 4ft tall), it’s worth raising them somehow; either using speaker stands or some sort of table. Keeping them close to the wall will help boost the lower frequencies, although a decent pair of hifi speakers (with 6-8" drivers) should push down into sub territory anyway, especially at higher volumes.
Most stereo amplifiers have some sort of auxiliary out, usually “Tape Rec” or “MD Rec”, which you can use to pipe your master signal into other rooms, which - as I said earlier - can be served using something smaller like a micro/mini hi-fi; the sort you can usually find in charity shops and car boot sales for £5. They won’t give you a particularly wide frequency response, but as anyone who listened to music as a kid knows (from their parents constantly complaining about how all they can hear is “duff duff”), bass travels through a house like crazy.
One legitimate use for PA speakers would be for the garden; nothing to stop you from getting a single cheap 12" active PA speaker (like the QTX ones) just for outside. You can then turn it down/off separately when it gets late so the neighbours don’t come knocking at your door with a hammer.
EDIT: Also, buy second hand wherever you can. You’ll save yourself a SHITLOAD, and unlike some types of technology, just because an amplifier was made 20 years ago doesn’t mean it’s crap or even worse than more modern gear. Class D amplifiers have been around since the 60s, and most decent quality amps are class AB anyway. Pretty much the only difference between an amp from the 80s and a modern one is that older gear is MUCH easier to repair/service. Instead of little microprocessors and surface mount components all crammed onto a single PCB, they generally use a more modular design with through-the-hole components and nice big solder terminals. In the unlikely event something goes wrong, it’s a cinch to fix; these days, manufacturers just expect you to buy a new one.
