Your about fully stocked, if you add anything esle you'd be overstocked. Plus the guppies will breed like rabbits and you'll have more guppies in no time. I had that issue with guppies in my ten gallon.
The neons won't be able to eat the guppy fry, plus the fry will hide in the plants. I have a male and female guppy in my 37g tank, but I have fish that a 5x bigger then them and I'm surprised my guppies didn't become a snack yet. 8 guppies will become 20+ in a few months.
If you can keep the guppy and shrimp populations down, the cory cats should be fine. The peppered ones seem to stay smaller than the bronze ones in my experience. You have a lot of plants, which will help with filtration. None of those fish are particularly messy.
So far I only seen 5 guppy frys.
Since I left them in the same tank, will they starve to death if I only feed my fishes flake food?
I do crush it up a bit, but i'm not too sure if they were able to see or even eat it.