What do you think of my setup?

You have to choose. Gouramis or Platies. Both would be too much for the bio load. As for the cory cats, they can actually reach up to 3-4 inches if cared for properly. They also are schooling catfish and need to be in packs of 5-6 which requires a much larger tank. Also, snails produce lots of eggs even without a mate( they are pregnant when you get them almost 100% of the time like guppies) So you would have tons of uncontrollable eggs everywhere. I would personally go for 2 gouramis and the shrimp. This is your best option. Also, you sound like a novice, so has your tank cycled yet? I think not. You will need to cycle your tank for a month while adding live bacteria cultures every week until that month is up. After the month, you can get fish. Look up "nitrogen cycle" on google and you will see what i am talking about.