1: In all honesty, I think it's based off the rating of the character
It's kinda shitty when you're going against a fighter will a higher rating because it lowers down your accuracy and avoid
2: Probably to the character- that was a pretty tough question wow
3: Yes
4: Galeforce, Limit breaker, vantage, pavise/aegis
5: Oh gosh I tried doing pairing just for ratings but I learned that it's funner when you do it based off the support/childs hair color
Personally, my favorites are-
-Chrom x Sumia (Bc Lucina and Cynthia are adorable as sisters)
-Chrom x Maribelle (Maribelle and Lissa are now sisters :^) )
-Henry x Nowi
-Frederick x Cherche
-Virion x Corderlia (Severa gets really shittastic status but you'll get a Hatsune Miku Severa! :D )
-Henry x Lissa
-Lon'qu x Sully
-Panne x Libra
-Libra x Olivia
-Cynthia x Morgan (Their supports are SO adorable ahhhh)