Changing bits:
There is a 3d printable “plug” on the not-store that will allow you to raise the Z axis, insert it in the semicircle between the maslow router clamp and the router, which pushes down on the button locking the collet. then you just use a wrench to loosen /tighten, then pull the plug back out and re-set your Z home by lowering the bit until it touches the workpiece, then set “z home” and load up and cut the gcode.
“Feeds and speeds”:
That will depend on your material, what feed speed you are using in your gcode, etc. There are a lot of good and very deep articles on how to set “feeds and speeds” on CNC machines that I’ll let you dive into. Basically what you are after with a router is chips vs sawdust (unless you are routing mdf then its all sawdust, lol). I’ll let others chime in on how they determine feed/speed; I’m by no means any kind of expert there…