Can't answer it all but a couple I will...

"JD DB80 32 Row CCS Planter with GS2 2600 for Planter Monitor, Variable Rate Population, and Variety Mapping"

The 2600 will currently do that as long as the planter wedge boxes aren't to old.

"Are the marker/fold/etc. functions on the new JD planters built into the GS2 or are they separate?"

The frame control and marker are controlled by a separate box.