This has confused me too!
So is the following correct:

• Each PC has a different Steemit/SteemD account, all valid and setup (or at least will be setup once start mining)
• However they all share the same WIF Private Key but all have unique "miner = NAME..." in each config.ini.
  -*So its PC1 has "miner= {kodachrome,SHAREDWIFKEY} and PC2 has "miner= [anotherminername, SHAREDWIFKEY| ?
• Only one PC has the "witness= " variable filled in (and its the name of that PCs miner account). The rest have no witness specified but use the shared WIF.
• All mining proceeds goto the account associated with the shared WIF Private key.
• The main Miner (the one with the most uptime) should be the Witness for your group.. otherwise if its off then you have no witness.

That correct?

Questions:

• Can the shared WIF key (used on all accounts) be any of the account's WIF key (assuming its where proceeds go) or does it have to be the Witness accounts WIF (aka primary always on miner) key?
• What is this setting for in Config.ini as its not discussed here:

WIF PRIVATE KEY to be used by one or more witnesses or miners

private-key =