What’s the significance of “PRO”?
I’ll best quote from this article:
In Samsung SSDs, PRO indicates the SSD uses MLC, EVO indicates the SSD uses TLC, and QVO indicates the SSD uses QLC. MLC, short for Multi-Level Cell, means that one memory cell can store 2 bits of data. TLC, short for Triple-Level Cell, means that one memory cell can store 3 bits of data. QLC, short for Quad-Level Cell, means that one memory cell can store 4 bits of data.
In general, the performance of Samsung PRO SSD is the best, then the EVO SSD, and finally the QVO SSD. The reason lies in the writing and reading mechanism of NAND flash.
I have added a $20 USB express card to give Windows it’s own dedicated USB controller
Is there a brand you recommend?
I am using the StarTech.com 1 Port Flush Mount ExpressCard SuperSpeed USB 3.0 Card Adapter (ECUSB3S11).
Does this add a 4th assignable USB controller?
Yes. 
[user@dom0 ~]$ qvm-pci | grep USB
dom0:00_14.0 USB controller: Intel Corporation 7 Series/C210 Series Chipset Family USB xHCI Host Controller sys-usb (no-strict-reset=true)
dom0:00_1a.0 USB controller: Intel Corporation 7 Series/C216 Chipset Family USB Enhanced Host Controller #2 sys-usb (no-strict-reset=true)
dom0:00_1d.0 USB controller: Intel Corporation 7 Series/C216 Chipset Family USB Enhanced Host Controller #1 sys-usb (no-strict-reset=true)
dom0:03_00.0 USB controller: Renesas Technology Corp. uPD720202 USB 3.0 Host Controller windows