You can use any PC to run pihole. The reason for Raspberry Pi is because it’s a machine you can set and forget, and leave it on for years at a time with very little power usage.

Don’t buy from Amazon, use an official reseller off the Raspberry Pi website. Only get an Amazon one if the price with free shipping is less than an official reseller + shipping; otherwise, you’re getting ripped off. Pi Zero W should be all you need, but if you want a little more power you can use a Pi Zero 2W.

You don’t need a monitor to run a pi. Most people run their pis “headless” without anmonitor, and you can google headless tutorials. However, you can use an adapter to temporarily connect it to a tv or monitor if you wish.