I wouldn't become too overly concerned with the carbon removing your trace elements. Since you are dosing non-Co2 parameters you WILL have to pay close attention to that, but 50% of the Activated Carbon Boogie Man Rhetoric is wildly exaggerated. I have yet to find any purity of AC that's any where near that level of efficiency.

With your particular tap water issues I would definitely consider one of the solid carbon ceramic water filters by Doulton.

Nothing wrong with DIY co2. The trick is to monitor the consistency of your Co2 output and rotate your yeast regularly to maintain a steady output. Not everyone can do that though. HTH. Prof M