A bit about level dependent benefits:

Health: 
Lv. 1 = 10+
Lv. 2 = 20+
Lv. 3 = 35+
Lv. 4 = 55+
Lv. 5 = 80+ (prediction --> no one has reached level 5 yet)
Lv. 6 = 110+
*the "+" is because with the use of health potions you can increase your health above the normal level

Base Defence:
Lv. 1 = 1
Lv. 2 = 
Lv. 3 = 
Lv. 4 = 
Lv. 5 = 
Lv. 6 = 

Base Attack:
Lv. 1 = 2
Lv. 2 = 
Lv. 3 = 
Lv. 4 = 
Lv. 5 = 
Lv. 6 = 

Heal Cost:
The cost to heal one point of damage is expressed in the formula: Cost = (Level*3)
So, to heal 1 point of damage:
Lv. 1 = 3
Lv. 2 = 6
Lv. 3 = 9
Lv. 4 = 12
Lv. 5 = 15
Lv. 6 = 18

Masters (hp):
Lv. 1 = Old Bones (35)
Lv. 2 = Master Chang (55)
Lv. 3 = Chuck Norris (100)
Lv. 4 = 
Lv. 5 = 
Lv. 6 =