Level 1 is as effective as level 20.
Defended? If so you’re a good flyer. Either that or the mages are not on a small isle.
At least 3 would be my recommendation. If 3, put them at the back of the small isle with 2 blues at back and red in middle. If 5 then blues on 3 corners and reds at the other two spots. This is to make it harder for attackers to hit all the blues and cloak to dodge mage shots.