Hi, even if you use a thick piece of "flat" aluminium plate with tapped holes you'll still have to use a dial indicator and shims to make sure it's laying flat.

MDF can be skimmed with a simple HSS fly cutter to make it flat and level........whatever cutter you use, it also needs to be rotating square to the table surface or you'll get ridges on the surface as one side of the cutter digs in etc.

Not knowing the design of the router, I would suggest that if the T slotted table extrusions were completely removed.......(if that is possible without compromising the strength of the machine frame)....... and a 20mm thick aluminium slab is bolted down in it's place, you could probably save a lot of money by just marking off the holes in a grid pattern and drilling all of them on the machine but only tapping them as needed.

Tapping with that router is not possible under power, so the holes would need to be tapped by hand, or off the machine with a tapping head on a drill press.

Once the aluminium plate is bolted to the frame and shimmed to make it lay flat, the surface will most likely need skimming lightly to make it dead flat as it's highly unlikely that it will be dead flat in the raw state........the router with a fly cutter should be quite capable to mill the surface flat with a shallow DOC.

If you opt to just put an aluminium plate on top of the existing Tee slot table you'll lose 20mm of Z height.......probably the simplest way to go if the height is not a problem.

The draw back is, with the plate laying on the Tee slot table top, it will soon get the holes jammed full of swarf, whereas if it replaces the Tee slot table the holes will be through and clear.
Ian.