I often thought of going the Linux way, but I really need my setup to as stable as a proprietary one. I know how difficult setting up a distro can be and how rapidly a Linux installation can break down. If you don't know your stuff beforehand, you'll spend countless hours on making your setup work again. For me, that's time better spent on literally anything else. I won't get into details because it's not Stack Overflow.
The second thing would be the obvious lack of software. The situation is of course getting better, but it still falls short of Windows and macOS. I've heard people using Ardour, most just emulate all the Windows software with varying results with Wine.
Just be advised - running a Windows emulator on a Linux distro can have way too much overhead for rPi to handle. Provided Wine even runs on rPi - its CPU is of different architecture than most computers have (ARM vs. x86/x64)
I think that going out of your way to buy any Intel-based MBP for cheap or just a capable Thinkpad with Windows on it will be a much better experience (in terms of stability and software quality) and will give you much more than a Linux distro can offer.
If you have some leftover funds though, I encourage you to buy a rPi and tinker with it, it's great fun!