Sorry, I don't have a lot of time to respond to this right now, but I wanted to point you to the
Make a paper backup! thread. It is a little verbose, but so was your array of questions
Short answer: if you never import keys, that paper backup is good
forever. Even if you use 13 trillion addresses, you'll still be protected with that backup (though the software might need to be adjusted to handle wallets with 13 trillion addresses...)
Distribute addresses like a maniac for 5 years. HD dies, get 100% of your coins back with that paper backup. The backup can be made at any time, but of course it is recommended to make it
before you use the wallet so you are protected the whole time you are using the wallet.
Cold storage is for a wallet. Put Armory on the offline computer, make a new wallet, export a watching-only copy of it, import that copy into the online computer. Now you can watch your coins, distribute payment addresses, verify payments without any loss if your online computer is compromised. And if you made a paper backup of that offline wallet, you are protected not only protected by the airgap, but you can recover from a hard-drive loss
any time in the future. Pretty sweet!
EDIT: The last thing I didn't mention was that the paper backup is also useful to recover your wallet if you forget your passphrase. Seriously, the paper backup is good for everything