I am going to chime in here.
I am one that if you get a mobile device with more storage I use it!
So, get an iPad with as much storage as you think you can afford.
FYI,
A 32 GBs will only have a usable free data storage space of between 24-25 GBs (you need to maintain between 2.5-3.0 GBs of free data storage space for iOS to continue to operate at nominal performance.
If you are planning to use this iPad for personal use, also, I do not know what else you, normally, use an iPad for, but 25 GBs of data storage space, while 2-1/2 times the amount of a 16 Gbs Apple iDevice, can still be a slim amount of storage, if you do more with an iPad than just teach with it.
If you want to minimise how much you use your MacBook, you may want to consider an iPad with 128 GBs (approx. 116-118 GBs of usable storage).