Onion Skin will work better has it holds all round and can be lot thinner.

To be honest Dave and no disrepect meant here and I know you have some experience with milling but think your kind of trying run before can walk with this.? By that I mean you haven't had much time using this machine so don't know it's capabiltys and your part isn't exactly new user friendly with those smaller cutters.

You may be better stepping back a little and work upto this part.

Also the Water cooled spindles above 12000rpm do have resonable amount of torque and shouldn't struggle with 5mm carbide tool while ramping only 0.5mm so are you sure you have the VFD parmaeters set correctly.?