It's got 32gb, I'm guessing the more you have, the less likely you are to run out with cubase and the better it will run. Been having a few issues today with crashes running thumbjam and cubasis together (awesome app for organic sounds btw) but I think it's because I've been pressing too many buttons at once hahaha.
Very impressed with this little iPad, I didn't actually buy it for writing music on, but very glad I came across cubasis.....who needs a computer!!
Oh and though you might think the mini is going to be too small, I've not had any issues really, even with my big calloused working mans hands