USBUART is a bridge between USB and the UART, easiest when you want to connect to a PC.
There are different versions of the UART implementation on PSoC5 a UDB version and a fixed-function version which resembles the SCB version of the PSoC4. The function of both are the same, APIs will differ a little bit. You are quite free, what to choose. When the very same codebase is needed, you will have to use the UDB versiuon which is available in PSoC5 and PSoC4 -42xx and -M versions.
Ok, I will make some tests and in case of need more help I will post more questions.
Thanks very much!