I'll let someone else provide the more conclusive an technical answer to your question, but I had no issue with using an external 10Gbps USB 3.1 drive to store my 1TB collection of RAW photos that I was also editing on the SSD. If you're just needing to store and access ordinary files, anything USB 3.1 or above ought to be plenty. If you're doing video editing off of it, you might need to upgrade to a USB 3.2 (20Gbps) spec drive.
The question of whether to have built in storage or external storage is your preference. Your external options are fast enough now that you're not likely to experience any noticeable difference.