1)
I can't judge, but there are some odd phrases natives wouldn't usually miswrite such like 心勝(必勝), 大元気(お元気) or 兄の御奮闘(貴兄の御奮闘).
2)
Both sides can be correct since those are basically written outward from the center of the flag.
3) a)
There are at least three dedications to 菅野 (Sugano or Kanno), so probably this is the name of the recipient.
b)
I can see only 仙台市 Sendai-city and 矢野田青年分団 Yanota/Yanoda chapter of a young men's association, but I can't find the place name Yanota/Yanoda.
c)
Seems like not.
Some parts are too blurry to read.