Looks great, brilliant effort!
I've had a long learning curve with therion over many years drawing up the surveys for St Georges, Montvalent. It took a while to figure out the best way to use it for a diving dominated cave. We've needed bits of metapost code for various things. I've had quite a bit of help from Torsten doing a similar thing with their survey at Cabouy. We've been swapping ideas on various things.
Our survey is here : https://www.dropbox.com/s/watp4mkphcsd1zj/St_Georges_1-1000_v1.4.pdf?dl=0
(Actually download it, the dropbox viewer is awful)
Would be really happy to help out with anything you want to figure out how to do, dive-line etc. No problem sending you our bits of code.
Anyway, my bits of feedback from a diver's perspective (I'm very much a newbie 'dry' caver) :
p.xxx m labels from dive base would be a good reference for overall scale & planning.
more contrast between sump/lake (air space above) would make it clearer.
legend says max depth 60m, but it's not obvious where this is(?) I assume this is a therion generated depth below entrance and not a mfw water depth? (Will become more obvious with the elevation)
the compass rose 'N' is really small and hard to see
the 'floor step' at the end of sump 2 - do you have a depth for the edge? would be handy to know whether you are deco in the shaft/rift(?) or in the surfacing tunnel bit. (From experience, these are some of the hardest bits to draw, lots going on in 3D)