I will look into those two options, I've used Kore a tiny bit recently, but didn't think to check if I could play from my phone. Though what I'm really interested in is being able to play the music while on the go using my data connection on my phone, instead of only being able to stream when I'm on my wifi ap. I will also look into UPnP, though I could very well be wrong, I believe it only works over a home connection..
I've looked into Plex, and I believe that's what I'm trying to achieve, but I'm trying to do it for free.. I've ran RetroPi before on this Pi, I couldn't find an easy way to install it from Noobs, but Recalbox also supports Kodi, so I could downsize to a dual-booted system, but I kind of like having things separated.
Thank you both for your replies.