Hey Blackhawk,
Wow, no CNC, no accuracy, and then such a price. I think I would not consider this offer.
If you have a CNC on top of the plate (I assume you found the positions to drill the holes for the four feet now), it would sound like madness not to do the drilling job with the CNC. But unfortunately neither the Makita trim router nor a usual 6,000–24,000 rpm spindle would spin slow enough to do the thread cutting job, and for the drilling job for the router it’s at the limit but worth a try on a sample workpiece. The Makita gets hot on low speeds (a spindle not, but you said you have none). I assume you don’t have the money for a spindle specifically for drilling 
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Here you can see once again that the manufacturers of the Onefinity lack foresight as to what benefit and what success a 43 mm mount would bring. With such a “Euro” mount, one would not only have a variety of milling motors as AMB (former Kress), Suhner, Mafell, etc. to choose from, but also a drilling machine with reduction gears. You could cut threads with it (in the lowest gear). I think when I will have my machine ready, I will try to mill a 80 mm → 43 mm reduction ring from the solid aluminum to be able to use such machines. Maybe for a drilling job at low speed, a 3D-printed reduction ring will do it.
Alternatively you could buy this 43 mm mount and file off the overhang until it is 80 mm in diameter so that it fits into Onefinity’s mount. It’s already 80 × 80 mm in size! Then you can mount your drilling machine with its 43 mm neck and drill the holes with a moderate rotation speed.
Anyway if you decide to do it, I would try it with the Onefinity, for the drilling job, and if nothing else is available, with the router, at the lowest speed and with cooling pauses. I would start with a very small metal drill bit (e.g. 2 mm) and then enlarge all holes with drill bits in 1 mm increments until the desired size. And with cutting oil, sure.
Note that for the tapping job, you not only need very slow speed (much slower) but also the ability of the machine to run in reverse direction (to leave the hole after cutting). So a usual electric drill with reduction gears is usable if you have speed regulation (in addition to the reduction gears). A spindle can run in reverse direction but you would need a very specifical low speed spindle.
Also I would not cut threads free-handed, but use a drill stand like this which you can move around everywhere on your tabletop. It allows more precision for vertical accuracy.
Here you can see a manual tap machine at work. You see that the operator switches into reverse rotation to leave the hole. The ugly noise that you hear when they finish a hole is the mechanical torque limiter which is necessary since they tap blind holes.
Note that when you cut threads with a machine, you need special machine taps that differ from those for manual use.
The magnet test? Steel contains iron which is ferromagnetic (as long it’s not austenitic stainless steel, which is not).
I would only tap holes if it’s steel, not if it’s aluminium. In that case I would use threaded steel inserts from the underside.