Scrap affects how much money you start with, how much you make each tick, and how much damage your towers deal.
Awards do not give benefits.
Increasing a tower’s level increases each of the tower’s stats by that amount (i.e. going from level 2 -> 3 will increase attack, range, and speed by 3).
Ascension will give scrap based on what level you are on, clear towers, generate a new map, and reset the enemies.
Tower upgrades are available based on how many are on the map. For example, every 8 Spitballs unlocks another Level Up to be purchased.
Different towers functionally only differ by their stats.
The level of the map is based on the number of enemies killed. Each level makes enemies stronger and faster, as well as increasing the number required to reach the next level while increasing the maximum number of enemies that can be out. If an enemy reaches the end of the map, it will begin refilling the progression bar. Level of the map also affects how much money you make when you defeat an enemy.