Google is now offering an additional space to accommodate 30,000 more songs and that is on top of the already subscribed for 20,000 song capacity. This is a free upgrade that is available to all Google Play Music subscribers. You can easily subscribe to the service by following the steps here and that is if you are not a member yet.
In case you want to listen to the music offline, then you can download your music to an iPad, iPhone or Android device. You can also access all your music via a computer on the web and the great thing about the service is that even when you upgrade to a new phone or computer, you will still be able to access all your stored music.
Though trends are showing a significant shift from downloading of music (moving towards streaming), there is a population that is unwilling to let go of their massive music collection and these are some of the people that Google is hoping to attract.
For easy use of the service it is best you use Chrome as it is already optimized for the service.