Howdy,
I have milled piles of Ni200. It machines well with soluble oil flood coolant. The minimum oil mist I have does not pull heat away fast enough an makes an irritating smoke. Sharp sturdy tools are a must. I don't bother with HSS. Speed can be your friend in the nickel alloys, but the low thermal conductivity of the Ni makes for high cutting edge temps; The limiting factor. The material will abrade cutters, but not terribly. The cutting edge temperature is the real killer. If you have experience milling titanium, nickel alloys are similar. Sturdy fixtures are important. Getting the most metal removed per flute engagement is key to milling economy, and tool usage economy. My advice, get a block of nickel and run your own tests using your programming style, your tooling, and machinery. My recipe works for me, but it is the result of years of failures and testing and is not likely to work in all situations.
Fantastic surface finishes can be achieved in Ni200/200 with good carbide and good practices. My favorite roughing cutters are Kennametal inserted button cutters with high positive insert, I run them using every last drop of spindle HP. Finish with solid carbide. If you can't see your reflection in your nickel parts there is still opportunity for improvement. Micromilling Ni and refractory alloys is the tricky part... all the normal rules break down when your roughing with a 1mm end mill.