Hi, welcome to the site.
A 10 gallon is pretty small, so you'll be fairly limited in your choices. What you have right now, most of it is not suitable for a 10gallon. Platys will get to 3-4" long and need 20gallons+ as adults. Your CAE will get to 6" long, and also would need a bigger tank.
I've never heard of headlight tailight tetras being agressive, but you need to keep several. They are schooling fish, and by themselves they are shy and unhappy.
You could look into upgrading your tank, but I think what you should do now is return the platys and the CAE to your petstore, and get some more appropriate fish for your 10gallon.
You could get some more tetras, so you have 6-7 of them. And then you could get a centrepiece fish - a dwarf gourami, or a male betta, for example.
You could also get a group of 6 small corydoras.
And you could definitely get some bamboo shrimps if you wanted, and/or ghost shrimp.
Above all, don't rely exclusively on what petstores tell you. Most of the time they are completely or partly wrong. If you see a fish you life at your LFS, I suggest you write it down, come home and research it before putting it in your tank.
Good luck!
Oh, did you cycle your tank? If not, you should read up on the nitrogen cycle.
