looks like ghost shrimp? their larvae need brackish water.
Not necessarily true. There are many species sold as ghost shrimp and not all of them need brackish water to complete the larval stage. Unless you have a well established tank you will need to supplement the food supply for them until they pass the larval stage.
Something pretty small like phytoplankton. Infusoria may work or even some of the First Bites fry food. In a decently aged and planted tank as long as they don't get sucked into the filter they should be able to forage for themselves. In my tank I don't do anything in particular to feed them. The numbers of them that reach the juvenile stage aren't huge, but they're definitely in there.