但是，這樣做，我將失去其他用途的GPIO（例如例如serial cable cable）。
I've used a Python to send out Serial via the USB port. So yes its possible. You need to install the drivers. I think the most common is FTDI. More info here on creating an alias and calling from python - Get USB address.
Installing the FTDI driver was buried in this doc... took me a while to dig it up.
The PiTFT will only use two GPIO Ports (#24 and #25), if you don't use the buttons (source). Of course, the board will stack up to all of them, but you can buy a stacking header which will stick through the holes far enough for you to connect other hardware. To make sure you don't use ##24 and 25 twice, you might want to cut them off after soldering.
And, since UART uses GPIOs ##8 and 10 for Tx/Rx, you should be good to go connecting to a serial console.
Another way to keep your GPIO ports clear physically is to use a GPIO extension cable or ribbon cable instead of directly soldering the board onto the Pi. Since the SPI pins (which PiTFT uses) are concentrated at the end of the GPIO, you can get away with a 5*2 pin or 6*2 pin connector.