For the offline wallet - is the information stored on the computer software itself or as a file? Would I be able to back up the wallet (file?) on an external hard drive? Will it appear in Time Machine (should my laptop crash or something)?
Also, if I store my bitcoins offline, does that mean I have to transfer them at home before I can use them for payment somewhere? Or is it meant to just be stored away for long periods?
For first paragraph the answer is Yes. Your laptop may crash if it has poor performance and with that if you install heavy offline wallets like Armory or Bitcoin-Qt. Yes, you will have to transfer at home. There are 2 meanings for offline wallet- wallet used in pc or laptop for daily use and wallet used in a computer which hasn't connected to internet. If you meant first one, then it isn't meant for long periods and the 2nd option can be used for both daily use(very very rare) and long period storage(mainly known as cold storage). You will have to sign a transaction and then push it if you are using an offline wallet(2).
~~MZ~~