@mogplus8 P5 and P7 are fine. The ADC's are limited to 8, P13 - P20, since only ADC1 can be used. P4, P8 and P23 are connected to the SD Card adapter on the expansion board. If you want to use the SD card, you cannot use the for other purposes. Otherwise you can use them. The USB is connected through a USB/UART bridge on the expansion board to UART0 on P0 and P1.