- I'd format the hard drive to get rid of preinstalled Windows OS
- I'd get these specs:
Do you think there is any possibility of hardware backdoor, or any leftovers from Windows, that would put my bitcoin at risk? I plan to use it as my main, home workstation.
Probably no hardware backdoors, but this is a good computer. This is probably going to your daily use computer, right? There are many other risks involved than only hardware backdoor.
As OmegaScream said, just buy a hardware wallet. It will be much safer, and you can use desktop wallets with your hardware wallet (such as electrum, for example).