every 5 or 10BTC ... use a new wallet.
i do this.
when you pay ... seller don't know if you have more than 5 or 10 BTC.
That would be very painsome, to manage 20x 5 BTC segements of wallets.
Besides the same way you created 1 wallet that can be stolen or hacked, all wallets can.
So unless you purchase 20 different computers and store it offline, then its a shitty method.
Why not just write it down on paper, and hide the paper in a plastic container under your sink, nobody will look for it there.