If you have Timer2 available, it can be used to generate higher baud rates with a 12 MHz crystal
Yes, if the other end accept the error in the baudrate.

Yoy CAN omit the 100nF across each chip.
You CAN get by without a supervisor.
You CAN run RS-232 with transistors to +5.
You CAN have an error in the baudrate.

does that make it right ?

Erik