RS232 / UART on Arduino boards/shield?

Dear all,
I have a question for my project... I need to add 4 (bi-directinal) RS-232 connections.
What boards (or shields) is best to use for this? (programming wise I use Python)

and is it possible to 'program' other ports (like the I2C connection) to act as a serial TX/RX port?
I know that I than need to lower voltages (RS-232 > TTL level)

If there are any people that know of schematics (online) it would also be a huge plus.

With kind regards,
Jeroen Wolf
from the Netherlands

Arduino Mega2560 has 4 HW serial ports.

and is it possible to 'program' other ports (like the I2C connection) to act as a serial TX/RX port?

SAMD21 based boards like the M0 are configurable like that; up to 6 serial ports.

Theoretical knowledge from the datasheet :wink: