The only reason to get 32 GB version is for video. Assume roughly 1 gig /movie. And of course, not every video needs to be preloaded into your phone, you can leave most of your library in your iTunes and just transfer when you want. I have a 16 GB and have never filled it up. I could, but am happy with the 16.
The apps and personal data only takes a tiny fraction - maybe 100 meg.