It seems that startlxde is part of lxde-common, which is not part of Lubuntu. So if you installed Lubuntu OS you don't have startlxde, whereas if you installed say Ubuntu Server and then added LXDE, you do have startlxde. Anyway I installed lxde-common in Lubuntu, and it all started working.
Except the user I get logged in as, doesn't have the settings adjustments I had previously created. This is something to do with /home/username/.config/lxsession/ having both /Lubuntu/ and /LXDE/ folders.
It wasn't too time-consuming to set up lxpanel the way I like it, and modify /LXDE/autostart to match /Lubuntu/autostart . I guess I will have to do that 4 times - 2 clients (with screens and keyboards) x 2 servers (headless).
I expect this could all be fixed up at the developers' end by adding a LUBUNTU entry to the dropdown list for Session Type, ( and a new set of bindings ?) This needs to be better explained in the blurb too.
That just leaves the armhf problem. I have found some hints on building, but I don't know what machine was being used that did it in 1 hour - building wxWidgets took 11 hours for me, and needed a big swapfile too. It would be much better if someone could do it once, centrally, and then maintain an armhf repository.
Anyway, x2go works nicely and I'll be sticking with it over x11vnc.