You should be able to boot from a small, fast SSD drive for system-like functions, and place your large files on other larger drives.
The Mac has always supported lots of drives, not just "the one drive". Lots of Video editors have been using a multi-drive setup like this for a long time. Source on one drive, Destination on a different drive, libraries or scratch (If used) on its own drive, give better performance because your workflow is not waiting for previous I/O to complete before proceeding.
If you can think of a more pointed question that would help you understand how to do this, please post it.