Seems like you're halfway home with VueScan, software that I have used for decades. Have you exchanged email with Ed Hamrick? Nobody knows more about scanners and printers and getting legacy peripherals to work.Connecting a printer or scanner to a Mac used to be so easy. Those days appear to be gone. I have lost the scanner function of my Brother DCP-9045CDN multifunction printer since I upgraded to Mojave. Brother shows this unit as incompatible with Mojave.
Vuescan allows me to scan with the flatbed, but scanning with the document feeder leaves horizontal black bars on the output. I had no such problems scanning from System Preferences -> Printers & Scanners in El Capitan.