Is there a max amount of data or songs that can be used with the free version please?
The short answer: no.
The long answer: there is no hard limit set, and there are people with over half a million songs, however, at some point you will reach a practical limit of course. However, I will be very impressed if you reach those 😉
Thanks @Koen. I'm really looking forward to seeing if Astiga can be a replacement for Google Play Music, and only for about 5 or 10k song, so it sounds like a tick in the box for me in this respect.