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 !
AC27 Apple Silicon. Twinmotion.
16" M1 Max MacBook Pro 32GB, Apple Studio Display, MacOS 15