The hardest part is running the wires through the walls. The rest is easy.
If you want just PC-only speakers on your desk/small area, you can generally just plug them into the back of your motherboard, so you don't need any extra hardware. However, it's incredibly rare for PC-only speakers to have long enough cables to reach around an entire living room.
As such, chances are you want standard theater-style speakers, and your own custom-length speaker-wire. If that's the case, just buy some 10 or 12 gauge cable from Amazon for a few bucks.
After that, I strongly recommend Ebay for lightly-used audio equipment and a receiver. People sell last-gen stuff for insanely low prices, and the hardware is still basically perfect.
You'll want to make sure your receiver can output HDMI 2.1, but otherwise basically anything modern should be fine for your needs. I find Yamaha's stuff is easy to use, regarding receivers. In terms of speakers, I prefer Klipsch, but there are plenty of other good companies out there.