I made a guide for using Fusion 360 for this here: Fusion 360 Guide For 3D Engrave
Theoretically setting up the first operation in Luban and setting an “Allowance” in the toolpath setting should work. i.e. set an allowance of 0.5, do a roughing pass with a larger tool like the 3.175mm flat end mill, then another pass with allowance of 0 to do the finish with a v-bit. Do keep in mind, Luban is not a very powerful CAM program, you’ll have to set your finish stepdown deep to do a single finish run, else it’ll air cut the full time anyway, at the same time, this means you can’t really control how deep the V bit cuts on areas with more leftover material and may break the tip. You’ll just have to do some testing.