Haven't flow the T-6 but I do have some time with the PT-6 series engine.
If you can visualize the reverse flow, compressor section spooled directly to the first stage turbine. There the spool stops and right next to the first turbine is another turbine: a power stage turbine which is geared to the prop.
N1: the speed of the first stage turbine and compressor section, in percent of rated rpm.
Np: the speed of the prop, typically in rpm's (IE 1700-2200 normal range for an early model King Air -90), but not always.
ITT checks as C-21 talked about. As far as EGT vs ITT, it all depends on where the designers decided to stick the probe (STS). For the T-56 that's on the Herc, it was at the turbine inlet (TIT), PT-6 it was around the interstage point (ITT), J-69: you get the picture.
PMU: sure, what C17wannabe said...