Reclaiming Harbor Freight milling Machine

Depends on the spindle. Some do a fair job of being a drill positioner. A few even do ok for very light milling. I had the older RF30 version. The newer ones are RF31s, although it may have an HF number on it.
I am no expert at rust removal, but I think anything that could remove rust from sliding surfaces without abrasion would be a good thing.

Surface rust is your friend on neglected machine tools, stops more serious deep pitting of surfaces. Only problem happens when something was piled on surfaces that holds water in contact for long periods of time. Any oil/grime left on the machine will help I would try a scotchbrite pad and some WD40 or paint thinner as lube Maybe finer grades of steel wool if it's really thick usually the rust layer is pretty thin. You can also lightly stone the bed to brighten it up. I beleive you can use evaporust soaked rags on surfaces to remove rust available at HarborFreight around here (Idaho) Many youtube vids on rust removal

Only the quill & spindle, dovetails and lead screws really matter. If they are OK you can mill the tabletop and its slots. Rust pits on the table top don't hurt, the vise rests on the flat surface between them.

I started a little work on it today, I'm happy to say that most of the rust is on just top portion where work get mounted, The is some on the other flat surfaces, but no much on the actually ways. I used a wire brush on most of it, after that I oiled it all real well and letting it soak. My next move is Lowes to get some steel wool and some smaller wire brushes. Mikek

Ya, it looks like it's not as bad as I had feared. Mikek

Fine steel wool is enough, you don't need to remove rust below the steel surface to use the machine. You aren't restoring a collectible antique.
My machines are 50+ year old antiques, whether collectible or not, so I do remove as much rust as possible. Instead of a '65 Mustang I have a '65 South Bend.