But, in case the user is done using the paper wallet and wants to transfer the whole funds, can my method above be used if bitaddress.org is run offline?
I mean, it
can be used, but it is still far from ideal and I still wouldn't recommend it. Running bitaddress on an airgapped computer will protect your private key during the process of converting it from hex to WIF. However, if you are then going to take that WIF private key over to your online computer and import it in to Electrum, then you are still exposing it to an internet connected environment. It's not quite as bad as entering it directly in to a live website, but it is still far less secure than working in a completely airgapped environment as discussed above.
Take an older PC of yours, remove any wireless modules from it and install a clean Linux distro on it. I'd personally recommend Debian or Ubuntu. If you don't want to
install it, then you could use it as a Live CD instead (Live CD means everything you do is wiped upon shutdown/reboot). For Live CDs, I'd recommend
Parrot OS which comes with Electrum preinstalled (or
Tails).
(bonus: I also recommend encrypting your HDD; bonus x2: if your future airgapped PC is old or you want it to run a lightweight distro, install Debian with XFCE).
Nice write up. There are a couple of things I would clarify here.
When installing a clean Linux distro on it, don't be tempted to dual boot or something similar. Format your hard drive first so that your clean Linux distro is the only thing installed.
If you are only going to be using this to sweep your paper wallet, then I would go down the route of a live OS. Unplug your hard drive in addition to your wireless components before doing this.
If you are going to be using this as a long term cold storage wallet, then obviously you should install the OS, but I would say that full disk encryption in this case is a must. LUKS is ideal for this.