grab that list of actors to spawn and save in a variable in the class. (toSpawn)
have a variable for how many actors to spawn per frame.
have a function that spawns actors (SpawnActors)
inside you loop the toSpawn array, from the last point until last+howManyPerFrame.
you spawn.
update last.
set a timer for next frame to the same SpawnActors functions.
if last >= total then return without setting a timer.