You wont be able to get the engine to iterate over much of anything in blueprint.
From c++ maybe.
Still not ideal.
Your harvesting system may need some tinkering or rethinking.
I say this as someone who has created several foliage responsivness sytems (DynoFoliage: UE4 Interactive Foliage).
The engine isn’t one bit friendly to loops.
Matter of fact, the only way you are really going to get something going is going to have to be via a custom thread and async calls…
I would suggest looking those up before even worrying about instances and what the engine does with them.