I have a lathe and a Milling Machine (had feed not power). Aluminum is easy to machine.

They have different carbide Bits for non-ferrous and furious/steel/iron for laths.

If you need to thread/tap aluminum regular rubbing alcohol passes for tapping fluid.

Generally speaking you don't want a casting. They are and have a grain Couse grain to them. However, an aluminum casting will machine OK.

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84 300D, 82 Volvo 244Gl Diesel

Hand grinder can do fine, use a flap disc and some wax. Just dab it on the flap disc while it's running, it'll help keep it from loading up, but that'll be way less of an issue with a flap disc than a hard rock. An ordinary candle will be fine. Borrowing your wife/girlfriend's Scentsy or whatever is not recommended.

That hard rock you just took off your hand grinder? Just throw it away. Flap discs are SO much more productive and the cost increase is minimal. Hugely made up for in the increased productivity.

If you or someone else is going to weld on it later, use a NEW flap disk, or at least one that's only been used on aluminum, and skip the wax.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

Is billet aluminum considered non-ferrous?

Correct, ferrous = containing iron/reacting to magnetism. Aluminum being non-ferrous.

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{2010 Mazda 3 266,000mi} - daily since new, Airlift suspension + some chunky sway-bars: fastest pass 17.7@77MPH
{1987 300SDL 256,000mi} - stock turbo @ 22lbs straight piped + a whole bunch of pre-turbo water/meth injection, 722.3 with increased line pressure, special sauce, and shift kit: fastest pass 16.5@82
{1992 964 Carrera 4 Frankenstein ??,???mi} - 993 forward dated, Speedster conversion, GT45 + E85: fastest pass 12.5@113

Yes.

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84 300D, 82 Volvo 244Gl Diesel

Billet aluminum is a solid block of aluminum. Billet aluminum parts are made by removing metal from the solid block by means of a lathe, mill, etc. to create the part. Cast aluminum parts are made by pouring aluminum into a mold. Most cast parts also require some machining for the finished product.