I know I am a little late to the conversation here, but I have been pretty busy. I wanted to throw in a vote, though, for Lumina Desktop. I got to see it in action at Ohio Linux Fest and it is really nice. QT based, which is good since I use a lot of QT apps, but way lighter on resources than KDE. I haven't done the actual comparisons yet, but I think it will beat out LXQT on resource usage.
It has some slick features as well. We won't be running ZFS on our Pyras, so we won't get the cool ZFS aware features, but it is a good desktop and has great multiple monitor awareness, which will be nice with that HDMI port.
As far as I know, it is either already ported to debian, or is at least darn close. By the time we are ready to start software testing, though, all that should be worked out.
ED, you may want to give it a quick test at least on the dev board to see how it compares to LXQT.