Ok. Thanks y'all for the input. I was tempted for the 64gb because it was available, but it seems that 16gb should be more than sufficient for my purpose. So I guess I hold on for a couple of days and see if they get the 16gb in store again. Like stated before, I'll have to be quick when they get those.
I also thought about putting pictures on it, but actually, this will and can only be a selection of all my pictures as the native raw format probably isn't supported and the files are about 12mb each.
As for pdfs, I mostly read something and when I'm done I delete the stuff from my mobile devices. A habit I started with my Sony readers due to memory restriction of the device. The Sony have the SD-Card slot, but this was rather slow. So I just went with the internal memory.
But again, thanks for all the input. Despite being able to spend the money for the 64gb, I think the 16gb model is the one for me. You guys are awesome