1) Can Super Elves/Dwarves be played on resource planks such as the banker's guild to collect double reward? Same for non-resource planks such as the Recruiter's guild?
No. Only when you gather can they act as double. if you use one on a plank your benefit is identical as if you placed a regular worker there.
2) After a player surpasses the 50 point mark on the score track can I assume the taxes continue to increase in a similar manner, or do you actually reset to zero tax?
I guess in 2p with a new player this is slightly more possible but still seems grossly unlikely to occur. Don't know official answer but I'd say that is a safe bet.
3) If I've placed all 12 of my property markers am I out of luck with building further? (In our game I just used another color's markers)
Not counter Limited. Use another color.
4) Can players place workers on planks on opponent's built properties? If not, does that mean the player has to pay the bank to place their workers on their own property?
No and Yes
5) In the Librarian's guild it says draw 3 and then discard one from your hand, Can your discard be from the 3 you draw? And can the 3 you draw be from the pool?
Yes and No
6) Regarding the property deck, do you have to pay a coin for drawing blind, or just from the pool?
You can either pay a coin to take one from the pool or pay a coin to randomly draw one from the top of the deck.