You are doing a heck of a job, much more overbuilt than most sheds. I commend you on all the time and effort you are putting into this shed....great work.
Blocks would not be necessary, but your criteria and tolerances have been so high till now, it certainly would not hurt. PT can be medium to very wet, so putting in blocks could help down the road, preventing any twist or warpage, although this would be minor. If you do it, stagger the blocks....example, first row put a block at midway (5 ft mark). Next row, put 2 blocks at 3 & 7 ft marks, and continue next row at 5, then next at 3 & 7....till the end.
For the span, most PT is typically pine or fir, or similar. If you check spanning charts, 2 x 8's at 16" centers should be good for at least 12 ft.....here's an online chart
https://www.awc.org/codes-standards/calculators-software/spancalc
As far as the knot goes, I think most framers would hammer through it. If they couldn't, they would move the nail an inch either way to avoid it. I think what you did is fine. If you really worry about these things, drive a screw within an inch of the knot, to avoid it. This would be only for **** people like me, that worry because knots do dry up and shrink, which might cause the nail to lift.
Great work so far. I think you will be very proud of the finished product.
EDIT, I just re-read and noticed the knot was for a hanger...just leave as it is, should be no problem.
