OK, here's another two:
1. When going smogless, what would you do with the big hole in the back of the lower intake?(red arrows)
smog-less has nothing to do with that hole. That hole is for the PCV line. (PositiveCrankcaseVentilation) There is a valve/line combo that goes from there to your intake manifold.
2. What is the purpose of this sensor?(Red Arrow)
IDK about that sensor, looks like (another) coolant temp sensor. take it out and see whats on the other side, see what it would be touching, thats what it's sensing. (compare it to your known coolant/air temp sensors)