Much depends on what you will be making on the mill. At the extreme end of least investment possible: decent vice (6" Kurt clone?) Set of parallels, set of two V blocks to hold round work in the vice. Small assortment of HSS end mills (2 flute for aluminum, 4 flute for steel.) A way to tram the vice (Dial test indicator & holder for the spindle?) 6" caliper. An edge finder, decent R8 drill chuck, set of R8 collets. Set of US name brand drills (115pc.) Some HSS taps for your most likely to be used sizes (don't get the carbon steel ones unless you are really good at getting broken taps out!) Tapping fluid, WD40 for aluminum to prevent chip welding. Safety glasses, acid brushes, chip brushes, spindle wrench if it didn't come with one. Set of strap clamps that fit the Tee slots. There are more things to spend a few thousand dollars on, get them as needed.