Sorry for the delay in responding - I missed your post the first time around.
Love the setup, very clean! The angle of the CDJs would kill me tho. ;)
Wow, 245K songs ... that could explain it. I have 52K songs (and even mine is bloated) and it took roughly 24hs to import. I found it was very quick through the first 40% or so, then seemed to slow down, and it could certainly have been due to the tracks it was hitting (many of them have multiple hot cues), or it could have been a memory leak. As you know, there is no way to batch process the import, it's open-it-and-wait (and this was one of my complaints about it) whereas the act of adding the new waveform data can be done at your leisure.
I'll pass this up to our rekordbox engineers as they may want to dig into things a bit further. I'm not sure if they tested the process with a library that large, but you're not the only one out there with that many songs, so it would be worthwhile to have additional details. Look for an email from the system re: the ticket, and thanks again for your patience.