A couple thoughts:
The 65mm VFD spindle is already capable of a lot. This was a test where I pushed it very close to stalling, but if you back off the speeds just a little bit it can be run reliably: https://www.youtube.com/watch?v=UqL-VyHb8l0
Yes a larger collet is nice, but in aluminum I would basically never use a 1/2" endmill unless I was doing light surfacing. Bigger endmills have to be run at lower RPMs, and you’ll fall out of the torque band of the spindle. The sweet spot for aluminum machining on a CNC router IMO is 1/4" to 3/8".
If you really want to push a machine that hard, you’ll also need air blasts (minimum) or some form of mist coolant because things are going to get HOT. I rarely push the HDM’s spindle to it’s max because then I need to stand 5 feet away to prevent getting burned by scorching hot aluminum chips. And that’s with it running on 110V and rated for “only” 1.5kW.
If you are making small parts, and will mainly be using smaller endmills, power shouldn’t be as much of a concern.