Would anyone speculate on the technical details of what Snowden probably recommended Greenwald do, step by step? What steps would you recommend to Greenwald if you had been in Snowden's position?

It's not enough to merely tell people "install PGP." Snowden presumably went into meticulous detail about precisely how to be completely secure. Even something small like "here is the exact exe installer to download" is probably significant, because that would mean that specific installer is clean and free of NSA tampering.