since you asked about setting combos
This looks like it will be fun when it's done. Plz see audio portal for cool loops to play for background music. My proposal for settings:
hero speed = 10 throughout entire game
level 1: # enemies = 10
# swarms = 1
enemy speed = 5
aggression = 0.5
After 25 kills
level 2: add a second swarm (in addition to the first one) where the new enemy has
# enemies = 10
enemy speed = 3
aggression = 1.5
(These enemies can be easily "kited" and sniped from afar, but will keel you if you get close)
After 25 more kills
level 3: add a third swarm with
# enemies = 5
enemy speed = 12
aggression = 0.5
(Introduces enemies that are faster than the player, but that aren't really much of a threat)
After 50 more kills
level 4: add a fourth swarm with
# enemies = 10
enemy speed = 9
aggression = 1
(I find that matching the hero's speed seems to make them tougher)
After 100 more kills
level 5: add a fifth swarm with
# enemies = 5
speed = 6
aggression = 0.5
but... THEY EXPLODE ON YOU IF YOU TOUCH THEM muahahaha
And keep adding more swarms with varying attributes as you progress.