1. The higher field strength from the new HTS magnets eliminates turbulence.
2. The ARC reactor will use a FLiBe molten salt blanket to capture energy from neutrons and breed tritium to be used in the fusion reaction.
3. The ARC reactor is designed to have a swappable 2cm thick vacuum chamber, which is the component subjected to the most neutron radiation (everything else is shielded by the molten salt blanket). These chambers are expected to last a year, and while they are moderately radioactive waste, the amount of material is relatively small and they should become safe in the order of a decade.
I highly recommend watching Dr. Whyte's talks on YouTube, he discusses the challenges, design, and performance in an approachable way. There's a timestamp index in the comments on this video: