This is probably a question for a longer discussion, less for an q&a forum :-) There are too many opinions on how to, based on the desired outcomes and values (and paranoia). The higher the values, the more important is a proper stress tested storage system. My current solution would be a mix of virtual machines and different hardware.
I think of storing several altcoins in several cold wallets (offline). My major concern would be data loss due to broken hardware. Therefor I'd have two or better three backups. I would create several offline PCs in virtual machines/environments, and also have an offline Linux, and maybe an older MacOSX and/or some RaspberryPIs (all offline). All systems have one advantage over the other. In the virtual machines I would try to setup a wallet, by compiling myself. If not, I take a default wallet. Once the procedure is "clean", I can do the same on an offline PC. It's astounding, how many dependencies there are...
I would install the default wallets on the offline machines, note down the priv keys and/or seeds, capture a photo of the priv key/seeds (make sure your mobile doesn't sync the photo to the network, and delete it after downloading!), and keep it written down and/or somewhere in a veracrypt container on the different offline PCs. It is good to distribute, hardly all break at the same time. Also I note down the public keys and/or addresses. Then in the exchanges, one could send keys to "my" addresses.
I wouldn't download all the blockchain(s), that is not required. For example in Bitcoin, it is sufficient to have the priv key, to get it loaded in an SPV wallet like Electrum. In Ethereum there is MyEtherWallet. Other cryptos only have the "full client", which make it a bit more difficult, when it comes to spending. The clients might not recognize the funds, which have been sent from an exchange to the cold storage since its inception. As long as there is no SPV type wallet, you would have to download the chain up to the point, where you received last funds, or assemble a tx yourself, and send it to the network. I have done this several times with bitcoin, but never for altcoins...
You asked for an efficient process, my guess is, there isn't. I leave it to the audience, to convince me of the opposite :-) There are too many dependencies and different requirements, even if you have the technical understanding, implementing a wallet and being able to cold storage still requires a good thinking on process and trying it out regularely. I'd be very annoyed, if I think I have saved my data, just to discover one day, things have changed and I cannot access funds!
Here in the forum are many links to the keyword "cold storage", and over at bitcointalk as well. So my post is not at all covering all and every options. Maybe people can share some more options.
