Hello,
I had partly success with sharing apk from a device with logged in google-play account. For this purpose I have “spare device” in my drawer… As I said, this methode doesn’t work for each of my payed apps - but for the most of them.
Yes, in short that’s what you have to do. As I said, it’s not possible for all kinds of apps you bought. Some of them check your google account to proof you paid. The data must be copied from /data/data/ via TWRP. Therefore your bootloader must be unlocked. More on this HERE.