I plan on using my iPad mini for school.
I'm going to get all my textbooks electronically, use pages, keynote, and numbers. I have some music, and quite a few apps.
Do you guys think I could use the 32 or a 64 gb iPad? I'm getting wifi only if it matters.
For reference, I have a 32 Gb (so what, 28.5 GB in reality?) iPhone and have 20 Gb used.
16 GB or 32 GB.
The amount of space on your phone isn't a good indicator of what you'll be doing with the iPad. For example, my iPhone is a 32 GB version and I'm using approximately 25 GB. I have 7 GB of music on there, 3 GB in photos, and a lot of app data (although I routinely go through and attempt to shuffle off older music, recorded videos, and unused apps). By comparison, my iPad is a more specialized device; I have 500 MB of music (what's the point of putting music on there when I have it on my phone, and my phone is always with me?) and 500 MB of photos (I use my phone for photos and videos, the iPad is a bit unwieldy for such things). I have a number of textbooks and articles, but those don't take up much space. My iPad is a 16 GB model.
If you're going to be using your iPad as an entertainment device, then things get a bit different. I don't store movies on my iPad, for example; instead, if I use my iPad to watch things, I stream them from my computer. Games tend to take up some of the most space, but I don't use my iPad as a gaming device - if you would, then that's another reason for going with more space. Lastly, you should consider your habits and expectations. Some people want to load everything onto the device and not think about managing how much space they have. Others (like me) are OK with occasionally evaluating what's on the device and then clearing up space. While the latter is more money-efficient, neither is superior to the other; you should determine what type of person you are and try to choose accordingly.
For what it's worth, I am out of the classroom setting but use my iPad with Numbers, Keynote, Notability (taking hand-written notes and occasionally audio recording as well), and I read textbooks. The iPad is used fairly strictly for those purposes, and 16 GB is fine for them.