No worries my friend. So about #2 and #3. I usually shoot wider open with the 85mm, and I was shooting manual. However, I noticed in image 2 (and these are roughly chronological) that I wasn't getting as much contribution of the flash that I wanted with respect to the background. Keep in mind that I'm shooting high speed synch here. So, I simply closed down the aperture, and decreased shutter speed, but not in direct proportion, in order to "force" the flash to work harder so that I get more of the subject illuminated by flash than ambient. It is a balancing act. I often shoot in the same location and vary settings quite a bit to explore different light effects in addition to different angles/distances with respect to the subject. It was a similar situation with images #6 and 7. The 85mm 1.4G gives me some latitude in terms of out of focus background because even with moderately smaller apertures like f/5.6, there's still pretty good isolation against background.
I actually haven't tried portraits yet with the 300. Not that I'm bothered by its weight too much, the thing is that when I shoot a person, I move around not only horizontally around the perimeter of the subject, going in closer and moving back, but I also go down lower toward the ground or stand up (I'm 6'3" so I can also shoot a bit down on people usually). With the small angle of view of a 300, I would be limited to moving horizontally. Some of my favorites shots are of models from a lower angle as I can isolate them against the sky or a wall and not have as much of a distracting background. As you probably noticed, I don't shoot with zooms. So when I am shooting I commit to one lens/focal length for quite a while then switch for a while to the 50mm but only if necessary (like I'm confined in some way). But that's an interesting question and I might try that someday (I usually like to travel just with one small bag so the 300mm of course requires bringing two bags).
So about the ever-ubiquitous -0.3 EC

When I used to shoot film, primarily Kodachrome, I would under-compensate the exposure slightly in order to do a few things.
1) Increase color saturation.
2) Reduce highlights (especially saturated ones).
3) Bring everything in terms of intensity down a bit to render the image more like a painting.
Japanese meters tend to over-expose a bit in my opinion as far as making images look overly bright and colors overly saturated. That's one thing that kept me away from digital photography for a long time. Now, I know the argument about ISO readings being equal across cameras (at least ideally). But now with these newer cameras, dynamic range is so high that one can also play with the sensor similar to what one could do before with film. So I like to do the same thing, I err on the side of the image, the raw image, being a bit under-exposed in order to bring everything in the histogram down a bit which gives me more latitude later on in Lightroom to adjust upwards if needed because adjusting a bright image downwards always looks worse than going from dim to brighter. The same holds true for highlights. I've never really tested how reducing exposure effects color saturation with a sensor, but the idea for me generally is to make the photo look more like a painting, in terms of the light. This is what masters like Ansel Adams tried to achieve in terms of having a certain spread of intensities within an image, and a large part of why he adapted sensitometry to the Zone System.