You wanna use the Arduino serial (UART) with a Mega 4808 board? No, problem. The Mega 4808 has three serial (UART) interfaces. Here you can read on which pins you can use the serial (UART) interface and how to use it.
You wanna programm the Mega 4808 or an other megaAVR 0-series microcontroler? Then you need a UPDI programmer. You can buy the Atmel ICE for ~100$ or you can make your own UPDI Programmer.
You wanna use the Mega 4808 with MegaCoreX and Arduino? Then you need the standard pin usage / pinout for it.
You wanna get started with the Mega 4808 in Arduino and you do not now how? Here is your answer.