HELP ME PICK MY NEXT FISH!!!!

A bit about my aquarium:
I've got a 20 gallon freshwater tank which currently has 4 smaller leopard corydoras, 4 bloodfin tetras and 2 fancytail guppies (I had two other guppies, but both were pregnant females and have moved on to another birthing tank.
NOTE: All fish are quite content and have been for the past 3 weeks. Very active and peaceful towards one another. My chemical levels are quite good and pH ranges from 6.9 - 7.1 most weeks. I have plants, driftwood and a cave for fish to hide in. Also, I have an airstone for plenty of oxygen.

Fish that I am currently considering:

1) 1 Dwarf Gourami ( I've been told that they do better alone in a peaceful community tank like this. I've always wanted one, but have been worried that it'd nip my other fish )

2) Yellow Platys (either bumblebee platys or sunburst yellow)

3) Longfin Danios (the type with the very feathery fins)


How many would you add and which type???

I know that I am getting close to capacity for a tank this size, so please help me choose.

I would skip the danios. I had 3 Giant Danios in my tank (I was told they were a schooling fish and would need the companionship). One of them died and the bigger one started chasing after all the other fish in the tank and killed one of my male fancy guppies.

Have you thought about a Molly?? I think they are beautiful.

Don't know the size of a dwarf Gourami. The one I had before was just a normal size one but he got really big!!

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10gal fry tank planted with Wisteria, Java Moss, Anuabis and Anacharis
35gal Sponge Bob tank with live bearing tropicals (daughters tank)
15gal planted with Swords, Java Fern, Wisteria and Red Rubin housing 10 fry and 2 bladder snails
55 gal with Oscar (future planted tank with angels and flowerhorns)
55 gal Community tank (platys, mollys, guppys, glass catfish, angels, phantom tetra, red eye tetra and swordtails)