there is 2 ways you can go. etch first then drill with the cnc, this will give you the neatest results if you do a good etching job. or if your lazy (like me) you can do isolation routing, use a small v tip and take out a small strip between tracks. how small you go is only limited by how flat your machine is and the size and quality of your tip. the results still look really good but sometimes the fibreglass of the pcb can be cut a bit deep. on my old CNC there was a bit of runout and one side of a large PCB (2’ sq) would be perfect and the other side would be cut a bit too deep, but its all about taking the time to set things up and leveling properly
Depending on how big the circuit is either way could be quicker too. small stuff is easily and quickly done by cnc. if your doing an A4 page of circuits and there are 1000’s of tracks etching is the way to go, or getting it made professionally.