as someone mentioned above,
first step is to work out your approach and what sensor hardware you’re going to need…
then look for platform that is going to support that sensor hardware. (unless you want to get into lower level coding!) and then you need to think about processing requirements if thinking about a rPI (the rPI is less powerful than a even a cheap laptop)
if you’re going for something like the rPI, then supercollider or pure data are good choices.
pure data i think is a bit easier for non-coders (at least initially) but as a ‘traditional’ programmer, I often prefer supercollider as its text based.
(that said, i find low level integration via externals easier in pure data)
as for bela… its great if you need analog inputs and outputs, and really low latency, but if you start hooking up things like usb based sensors those advantages tend to diminish. also the beaglebone black is much less powerful than a rPI3/4.
(btw: i dont think the bela ide helps with pure data, but it is very cool for c++ and supercollider)
so if your not using that, id use rPI and look at the patchboxOS by blokas as an easy to setup distro for audio work. (if your doing audio on the rPI you’ll need an audio interface - checkout pisound)
the nice thing is… if you’re doing it in pure data or supercollider, then you could do initial development on your desktop, and then you’ll have a feel for the processing load, and if moving to a rPI is viable or not.