Hi Cary,
The new Mac Pros are designed to work very efficiently with external hard drives connected by 'Thunder Bolt': Effectively as fast and 'available' as internal Hard drives.
And to second ejrolon, Macs have been able to run multiple instances of AC for some time now: On a new Mac Pro I would imagine that it would do so with great ease !
AC25. Twinmotion.
M1 Max MacBook Pro, MacOS12