Nice render.

Ringmaster tried to turn their spinner into a giant bearing. It didn't work out so well. One hit and it generally deforms everything enough that the bearing jams up. I could see this being an issue with a giant aluminium bearing as well. The only ring spinner I've seen that can take knocks and keep running is warrior from Team Whyachi in the US. Even that has trouble at times. Your bearing races should really be steel.

I also think you are gearing it to go far too fast. Granted I don't know the ins and outs of the design but a very quick and nasty calculation using the team cosmos kinetic energy calculator puts your kinetic energy above 100kJ at 3000rpm and over 500kJ at 6000rpm. These numbers are insane (for reference these are larger than carbide and tombstone). All this energy has to come from somewhere and your motors will only delivery so much in a short period of time. At 6000rpm the current draw on the motors would be enormous as the disc fights with the air resistance at that speed.

At 3000rpm your cutter speed will be approx 245mph with a 70cm dia disc. At 6000rpm your cutter speed will be approx 491mph.

You also have to consider cutter bite with a spinner. This is essentially the time taken between one tooth leaving a position and the next taking up the same position with how much forward movement the robot has had during this time. I've posted about it in the past but essentially working out the length of time at a given rpm for one tooth to rotate and another take up the position. Then I tend to use this time with a forward robot verlocity of 1m/s (conservative but realistic at times) and calculate the distance the robot will have travelled. This is your cutter bite. It is independent of disc radius and is only dependent on forward motion and rpm. Bigger cutter bite is good as it means more of your tooth can get into your opponent and transfer energy. Too little and you end up grinding away on your opponent.

Your plans are ambitious which is good but I'd bring it back just a little bit and slow down the disc a bit. No need to go so fast as you will in all likelihood either never reach those speeds or reach them once, hit something and then never work again.

As to the question regarding ali etc I would recommend going with the hardox over the HDPE for a heavyweight