And how often should I back up? Every 10 transactions? Every 100?
Or every 3 days? week?
Can't I just make 1 back up, store it in a safe and forget about it?
I store the majority in a cold wallet (usb offline) backed up to my email. Update it once every now and then if you want or when you need to deposit/withdraw more coin.
What if I back up my wallet in the USB with 10 Lite coins for example.
Then on the same wallet on the computer I buy something for 10 lite coins which turns it to 0. But the other wallet copy in the USB still has 10.
Does that mean when I use the Wallet in the USB on another computer it will synchronize with the network and update to show 0?
Or is it the other way around that a new Wallet and address will be made for receiving coins since I moved my backup wallet to the USB?
Yes your ltc is already spent and if you try to send it will be denied.