I followed the instruction for cold-offline in BitKey and created my cold wallet on a USB key with BitKey burned and booted from a CD-ROM. I noted the encryption password and the seed phrase on a paper which I will store in a secure location.
The workflow described on the BitKey website would use cold-online mode for watching the wallet (and preparing transactions).
Now, is there anything wrong in adding the watch-only mode (I think BitKey stores the proper information unencrypted on the USB key) to my normal work PC running Electrum on Win 10?
In my opinion, it shouldn't because no single secret will be exposed. However, I am wondering why the documentation is so keen on emphasizing the workflow with cold-offline and cold-online.
Lastly, I intend to store my Bitcoins for long term. In 10 years I may have forgotten details about the sofware, BitKey may not exist any more, I may not have a CD drive any more, Electrum may be at a completely different version and who knows, it may be hard to import the data. For that reason I really love the simplistic idea of paperwallets. But individual paperwallets are hard to deal with. Hence I would like to store an export of the public/private key list of my wallet as well. I feel this format will be most barebone and most likely to be importable also in ten years or more (I know that the seed could re-generate them but I hope you get my point).
For backup purposes, I also want to store the AES encrypted contents of the USB key on my NAS. I am thinking of packing the public/private key export into this file as well. Using a very long passphrase and storing it in a KeePass database.