There is nothing wrong with running openhab in docker, if you want better reception there are examples in this forum how to connect a usb stick through ethernet. Docker is great actually, you can spin up a HABApp container alongside and use easy and flexible rules.
If you are going to buy a new device however, I’d recommend at least a Pi4 or a used HP T620.
Why not get two sticks that are well documented and tested? Also if one fails, the other one will still be working.
That being said, I’d try to setup openhab on my local (main) machine and make some first steps with it before offloading to a dedicated machine. Tinkering with both the hardware and software can get overwhelming quite quickly - especially if you are new to openhab and linux.
If your actors and sensors are working you can just move the existing configuration.