The platy will mate and likely the fry will be eaten. I have a bunch of Rainbow Blue Platy which I brought home and bam! three of the fish had babies! Some of the babies I saved, and I have appx 8 (the growing up babies and one adult) in one tank and 5 of the original ones in the other tank.
These fish are very active but I have never seen them hurt each other. Though I have heard the same thing about being aggressive.
In your proposed stock plan you don't have any bottom fish. So maybe start thinking about what might be good for you.
I would look into some dwarf Cories after the tank is stabilized and been running without problems for a few months. They like to be in a shoal and about 5 is a good number, they are pretty small so you could probably add 4-5.
The Long fin Danios should have a little higher number for the school
As for the Cherry Barbs, I understand they can be nippy if not in a big enough school, I am not sure what number that is though. I have just had one cherry barb given to me when I adopted some fish.
Also I would add the fish in groups slowly.
Spend a little more time at the fish store(s) and see which fish are the ones that draw you in the most and build your stock from your absolute favorite.