OK, one more question. Would it be OK to send the post-mixed BTC directly to a merchant from the mixing service? Say you wanted to pay for a VPN or Email annual service via BTC. They would provide you their wallet address for payment. Is this not a good idea? Or is it a great idea because you aren't personally touching the mixed BTC?
Nothing wrong about it, just make sure you calculate the correct amount.
I don't know for sure about it, but personally, I prefer to keep the mixed coin on my wallet first. It doesn't matter If you personally 'touched' it, the mixed coins should be still untraceable. AFAIK, The Electrum wallet only shows your IP address and public address, make sure you connect it via TOR.