Re: SD card
I'll answer this one for you to,
Some of us are in really to music and have an awful lot of it. I've got about 500 12' vinyl dance records. With an average of 3 mixes per record that lot on their own is 1500 tracks.
Then on top of that I also have about 1500 cd's (of which 98% are albums). Each CD probably has on average 10 tracks ((most have more but I'm being conservative) so there's another 10,000 songs. However, at least a 3rd of those albums are double cd (or more) albums so that's at least another 5000 tracks.
So I've got at least 18,000 tracks in my collection and I know I am being conservative with my figures.
Now on the second part of your question. I don't listen to them all at the same time, I chop and change often, some songs / albums go years without being played. But then one day I'll decide I want to listen to one, do so, get back in to it and then decide I want to listen to it when out.
My phone only has 4S only has 32GB of space so I end up having to clear an album on the phone already to fit the one I want on there on. For me it's no great issue as my entire library of music is already ripped (I spent a long time doing it a long time ago), but it would be convenient to be able to fit everything on in one go.
PS, the reason I have an Iphone is simply that I like them, I like the music player on them and for a long time they were apart from sony devices the only devices which would play gapless playback. My library was ripped in apple format years ago when I had an original ipod and I'm not about to spend years changing it.