>About the question 3, I need the three serial ports.
shouldn't be an issue at all
>According to question 2, the TTL serial port, manage the standard UART protocol, isn't it?
Yes, just not PC appropriate signal levels, that's why you need MAX232 to connect it to a PC.
UART1 and UART2 already have this level converter and DB9 connectors on the developepment board. UART3 is brought out to Header X19 (same area on the board) and is indeed TTL.there are of the shelf products that will let you connect it to a PC.
and probably more and cheaper ones on ebay
or if you PC has no DB9, you can go directly to USB: