Hi Benuvel Victor
First of all, MK20DN32VLF5 and MK22DX128VLF5 are old devices which are not supported in our SDK, this means that they don't have USB firmware available. MK22FN128VMP10 and MK22FN128VDC10 do have support in the SDK and they are fully supported with the latest USB stack.
will it work independently as USB host?
Yes, they can work in USB host mode.
If so, how this is configured?
you can find USB host examples in the SDK package, you could check those examples and see the implementation, also, for your reference, you could check the Reference Manual and also they are some Application notes for USB host functionality on kinetis devices.
Is Firmware fully supported? (Preferably in C language)
Yes, SDK package is implemented in C language.
Is Ethernet over USB class supported?
The ECM is a Sub class implemented with CDC class, there is no an example for this implementation, but you can find a HOST_cdc example (using Vcom ACM).
What about driver source code and APIs for my MCU?
Yes, as I mentioned, in the SDK package you can find drivers to control the peripherals in the MCU, including USB. You can download the SDK in our web page: Welcome | MCUXpresso SDK Builder
Hope this helps
Best regards
