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.
I also do this exact same thing. I have wallets of various sizes between 2 BTC, 5 BTC, 10 BTC. Never larger than 10 btc.
That way when it comes time to spend, I can pick the closest wallet size to what I need the BTC for, and leave the rest safe and untouched.