How is it possible to buy and publish a Q1 paper?
This sounds like a scam, so I doubt you'll get whatever they promise
It's possible (though unlikely and unethical) for anyone capable of producing the research to exchange money for an edited author list, but the problem of finding a buyer in the same area of your expertise is not trivial and probably doesn't make for a profitable strategy unless... See above
Absolutely yes. It's plagiarism to claim someone else's work as your own, even if you pay them for it.