Leveling up Spirits

[Boozie]

So I'm looking for any advice people can give me on which Spirit abilities to level up from the point of view of a paladin on normal.

I know rage cost decrease is good and rest decrease is good, but at what point do I stop leveling ability X because I don't want the rage cost to go up?

Are there any specific abilities I should focus on leveling?

Are there more than 4 abilities? Do I need to pass on a particular one in order to gain different ones? I'm assuming no but just wanted to make sure.