Encryptic,
There is a famous phrase in Dune: "Plans within plans within plans".
If applied to Wolfe, that might be the understatement of the century.
I've told numerous friends (though it's kept a few from making the effort) Wolfe tells you 2/3 of a story. The other third is implied and left as an exercise for the reader. Numerous scholarly works have been written on Wolfe's New Sun. I'm the first to admit there are layers I've yet to divine. It doesn't help that like any scholarly subject, there is an extremely overly-healthy amount of disagreement.
What Churchill said about the Soviets; "A Riddle, wrapped in an Mystery, inside an Enigma." also applies to Wolfe.
Regarding your question about Long Sun and Short Sun. There are a huge numbers of ties and allusions the New Sun series. I really enjoyed both, but they are VERY dense, and occasionally, dry. Long Sun holds the distinction for my favorite Wolfe line ever though:
"Laughter filled her as the summery sunshine of a year long past descends gurgling to fill a wineglass."
If you've enjoyed the book of the New sun, remember that Wolfe writes for the
Re-reader. Every time, you'll find something new. Try keeping in mind the next time you read the New Sun, it seems that Humans are all given Saint's names, while Aliens (pardon me, musn't be rude, Hierodules) are given names drawn from mythology. It makes certain aspects of the story quite....unusual.
As for what's in the Mine? My guess is an early Talus, put there by the original owner of the Homunculus in the Citadel Laboratory that also held the fabled "
Emerald Bench".
What's a Talus? Who's the original owner? Enjoy the Book of the Long Sun. Say hello to Silk for me when you see him.
Good Silk!