Hello, I can answer question number 3 because I have been trying to figure it out on my a7RIII all day and finally cracked it! MM -2.0. You are seeing this in the bottom of the live view screen, right? It's the exposure value. If you look through your viewfinder exposure looks like (simplified) this: -3 -2 -1 0 1 2 3 and the tick would be on the -2.( under exposed by this value). If you had MM -1.0 the tick in the viewfinder would be at the -1. I hope this helps.
I have a sony a7rIII and a 1.4 Gmaster 85 lens. Things were fine, then I bought a 24-105 lens, played with it for several months, then I put the Gmaster back on and now I can't change the aperture in manual mode. If I put it in A priority it seems to be ok. But I rarely use that. Has any one seen this before. 'can't figure it out.