Re: Deciding between 16GB and 32GB, how much memory is enough (for apps, etc.)?
The decision depends on how you use your phone.
Mine is basically new, and I have about 9GB of the 16GB on my phone free.
1.7GB is consumed by app data and media (I have a few music albums pinned in G+), and a lot of apps loaded.
The other 5GB is the OS itself, so you'll never have more than 10-11 GB free for what you want to store.
I can't fit my entire music collection, but I can pin a handful of albums while on WiFi and have a reasonable selection of music for when I'm on the road and don't want to blow my 5GB monthly bandwidth allocation listening to tunes. I can't fit a ginormous library of photos, but I can take a few hundred with me if I want to.
16GB is sufficient for me, and the price difference was enough (for me) that I chose not to spring for the extra space.
If you can afford it and think you might need it, more storage is never a bad thing to have.