Another handful of questions popped up today that I'm hoping the community can help with.
1) As an example, does an arrival effect count as an ability which would prevent it from getting the +1 bonus from Midori when Midori is leveled up to the middle tier?
Yes. Any non-flavor text in the abilities area of the card counts as an ability. "Unit type" (such as Cute Animal, Illusion, Soldier, etc) does not count as an ability.
2) Do long range attackers have to attack the squad leader? And is long range considered targeting (highly doubt it)?
Yes to the first, no to the second. All targeting effects have targeting icons.
3) Does the tower hit long range attackers (I believe it does)?
4) Can you use all level abilities when a hero is max level or are you limited to only the ability your current level is at?
You can use all abilities of your current level and the levels below!
I know they're working on some ruling documents, but there's a spreadsheet of rulings up at sirlin.net/rules that has a lot of stuff in it.