There is no way to change the unit cap or how many units spawn at a time, but you can change the cooldown with ow_cooldownscale. With ow_damagescale_npc and ow_damagescale_players you can change how much damage NPCs and players do.

Do you have to happen a list of all this gamemode's cvars and their default values? Thank you.

ow_maxrounds 10
ow_timelimit 1800
ow_damagescale_players 1
ow_damagescale_npc 1
ow_allow_spectator_control 1
ow_cooldownscale 1
ow_multiple_overwatch 6

Thank you very much. Appreciate it.