Programming with the RS-232 port is easier than an USB port?
If your PC has a RS232 port, be happy and use it.
If it just has USB ports, easiest is to connect that directly to the Arduino. You're doing serial communication anyway, either with a physical port or with a virtual one.
Serial Speed is not limited to 9600 ( about 1000 bytes per second ), BTW.
But sending 0 or 1 500 times per second is not the optimal solution. Arduino can do some of the work you intend to have done.
Every second a number between 0 and 250 is probably better ( and easily doable with default speed ), if you just want to know the pulse rate...
Rather check that your loop() cycle length is short enough to catch every state change of your pulse. If 250 pulses per second means every pulse is at least say 1 of 4 msec in either on or off state, you should be on the safe side. 1000 micros in one loop round is a lot for 16 MHz Arduino Uno, no need to go for interrupt handling.