It means you get 10% whenever your general is hit. If you get hit 3 times in round 1, you'll still carry the 30% on round 2 and so on. It's great for battles you can't win in 1-2 rounds.
Level up the rest of the buildings, if you finish those as well, you won't need your money except for trades, research, and forging weapons. You'll probably get a shitload of unused coin if you finish research. xD
Notes and armor, yes. Musket, no.
Not really. I already got 36 clovers. Only need 4 more for UR evo. Equipment is only worth it if you still haven't got mumei and World Boss equip.
Yes.
Try going on server 3. :P Less pros more noobs.