I have BiaB installed on a 2TB Thunderbolt 3 external SSD. I just did a standard install to D:/bb. /Drums and /RealTracks are folders under /bb. As far as keeping work on the desktop and laptop in sync, I'd just use the /Songs folder under D:/bb and move the USB drive between the desktop and the laptop. No need to have a separate install of BiaB on the desktop.
Also, I'm just wondering why you felt the need to use /BBData and not just go with the default file structure. It's not like you're trying to use two different drives and splitting BiaB between them.
I never liked the default of installing BiaB into the root of my C: drive. Not a problem now that I dumped my 120V desktop and bought a ThinkPad with the standard multi-voltage power brick when I moved to France. I have a 1TB internal SSD, a 2TB external TB3 SSD, and 2 external 2TB USB3.2 SSDs. Now my 17" ThinkPad with a 4K display and the Thunderbolt port extender is all I'll ever need.
EDIT: My first professional programming was in 12-bit octal assembler on a PDP-8e (that last one with a wirewrapped motherboard), a 1 MB 14" unsealed HD, an ADM3 terminal, the TED line editor and a 3-pass paper tape assembler. The PDP-8e had 32K of non-volatile core memory and the bootloader had to be manually entered via paddle switches on the front of the CPU box. We've come a LONG way!