iPad aviation apps?

Usefulness of iPad aside (there's another thread for this), if you have one and use some EFB app(s) with it, how much space do they require? I am considering getting one and understand I need the 3G version to get the GPS receiver. But I am trying to decide if the basic 16GB model would be enough to store all the charts, etc once I take it flying with me.

i use jepp flightstar on my lenovo tablet. not sure how much memory is required but i have all charts for the US loaded. i'll check on it next time i'm at work but it may be more than 16gb.