As long as the computer can run any version of Windows, you will be fine. This USB controller can be used with the latest version of Windows (11 at the time of writing this answer) and you can use 64 or 32 bit modes.

You will see that Mach3 is recommended for 32-bit ode, but this information only relates to controllers that use the parallel port.

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[72] What are the CPU requirements for Mach3?

Yes, this controller can control the spindle on and off, and control the spindle's RPM. Here are two videos that show how to do this:

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[72] will this software include any drivers needed to make the computer talk to the VFD?

Mach3 is a widely used CNC control software. Depending on the CAM or CAD (with CAM support), there should be a post processor for Mach3 built-in.

If you are writing your own g-code, Mach3 has an extensive list of g-codes and m-codes which is listed below. This list comes from the Mach3 usage manual in chapter 10 Mach2 G- and M Code Language Reference (https://www.machsupport.com/wp-content/uploads/2013/02/Mach3Mill_1.84.pdf).

G0 - Rapid positioning
G1 - Linear interpolation
G2 - Clockwise circular/helical interpolation
G3 - Counterclockwise circular/Helical interpolation
G4 - Dwell
G10 - Coordinate system origin setting
G12 - Clockwise circular pocket
G13 - Counterclockwise circular pocket
G15/G16 - Polar Coordinate moves in G0 and G1
G17 XY - Plane select
G18 XZ - plane select
G19 YZ - plane select
G20/G21 - Inch/Millimetre unit
G28 - Return home
G28.1 - Reference axes
G30 - Return home
G31 - Straight probe
G40 - Cancel cutter radius compensation
G41/G42 - Start cutter radius compensation left/right
G43 - Apply tool length offset (plus)
G49 - Cancel tool length offset
G50 - Reset all scale factors to 1.0
G51 - Set axis data input scale factors
G52 - Temporary coordinate system offsets
G53 - Move in absolute machine coordinate system
G54 to G58 - Use fixture offset 1 - 5
G59 - Use fixture offset 6 / use general fixture number
G61/G64 - Exact stop/Constant Velocity mode
G68/G69 - Rotate program coordinate system
G70/G71 - Inch/Millimetre unit
G73 - Canned cycle - peck drilling
G80 - Cancel motion mode (including canned cycles)
G81 - Canned cycle - drilling
G82 - Canned cycle - drilling with dwell
G83 - Canned cycle - peck drilling
G84 - Canned cycle - right-hand rigid tapping
G85/G86/G88/G89 - Canned cycle - boring
G90 - Absolute distance mode
G91 - Incremental distance mode
G92 - Offset coordinates and set parameters
G92.x - Cancel G92 etc.
G93 - Inverse time feed mode
G94 - Feed per minute mode
G95 - Feed per rev mode
G98 - Initial level return after canned cycles
G99 - R-point level return after canned cycles

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[72] What G codes are supported