1) they all get the Standard Pack of being stronger/more durable/healing faster, but beyond that, nope! their abilities are as unique or generic as you feel suits your character

2) yep

3) nope, all the mahous can see/communicate with all the spirits (when manifested - a spirit can choose to hide itself if it only wants to hang out with its specific partner, or hide itself to block interaction entirely. they can be as friendly or moody as you like)

also that sounds great! i'm excited to see what you come up with