1) Oddly, and this theme will be repeated, the extent of my sake tasting is just too limited to answer. I'm honestly, after about 3-4 years, still at the stage that I've liked all sake I have tasted. That said, I'm leaning away from Nigori currently. It's ok, but not my favorite. Right now, mostly because I have 'discovered' it three times (I'll remember this time ) and liked it each time for it's 'earthy' flavor. Bunraku Nihonjin no Wasuremono Yamahai Junmai.
2) At this point, I simply don't know. Insufficient data. What I will say is that I've hunted down a couple 'random' Yamadanishiki based sake...and whereas they were quite good, they were so 'delicate and refined' that I am not sure if a) I don't have the refined palate to fully appreciate them b) I like a more full bodied (but not sloppy) sake c) they were bland. Right now I would again go to Bunraku Nihonjin no Wasuremono Yamahai Junmai but mostly because I know I like it. More tasting is needed.
3) Junmai I believe.
4) In that I am on batch 3, again 'insufficient data' is the answer. My virgin brew 2 years ago was an unmitigated success...but I credit that 90% to Eckhart and my ability to follow directions. Keeping all other things equal, I have two more batches going. The first with my own koji via Vision spores and Hitomebore , and the 2nd with a different koji and spore, and 60% Akita Komachi. Yes, those are pretty big changes, but what is consistent is temperature, time and addition schedule. Basically, I am gathering my own data for what makes for the most significant flavor impacts.