I was helped through some of these start up issues by having a very good teacher way back in junior high school watch all that I was doing and evaluate results after every roll. We used the school's film, had to use the same camera for the semester, and basically it was all about eliminating variables. This has carried over to my more recent darkroom/processing work at home, and while I have experimented more than I probably should have with different film, much of my process is the same for each roll.
It sounds like you've gotten a lot of the basics honed in and are almost there, so keep at it. Maybe shoot only the Nikon for b&w at home until you get the Hexar figured out.