Haha, glad I could help! 
GPU particles should be used in as many cases as possible because they can render without needing any CPU support or hogging CPU cache memory (there is a small CPU usage for spawning, but that happens very fast). Epic said you can have millions of particles, but I’ve been noticing that in the hundreds of thousands you’ll need to make the particles smaller than a pixel in order to notice them, and making them any larger would create massive overdraws of transparent particles overlapping each other.
I am really, really excited to see this game! Good luck! 