Probably a stupid question, but am i correct in thinking that I can connect an external hdd and install my wallets (bitcoin, dash, litecoin and etherium) onto the hdd which will then sync the blockchain whenever I connect the hdd and open the wallets?
So this would technically be a form of cold storage?
Also.. if i have already installed my dash and litecoin wallets onto my macbook, should i bother copying the install/root/files over to the hdd or should i just download a new wallet onto the hdd, trans all the coins and do it that way?
Hope this makes any sense
Yes, You can connect, but you have to make sure that your computer is safe before connecting your wallet! I guess that online wallets with 2fa authentication/email authentication can be safer than that every time you login your wallet it will ask you to confirm email there are many more security options you can add (blockchain.info)
In my opinion you should save your DASH and litecoin wallets separately. It would be good in my opinion.
Also, As TryNinja mentioned you should disconnect your computer from internet first then do anything. Offline wallets are much safer in that way.