#Esp8266 firmware that uses mac
Windows users will use COM3, COM4 and similar, Mac and Linux users will use /dev/tty.usbserial- or similar
#Esp8266 firmware that uses serial
And it has to stay pulled down all the time. It has to be done by pulling GPIO0 to the ground and then powering it up. To flash ESP8266 it has to enter flashing mode first. Note about LM7833: it has 2V dropdown voltage, so to provide stable 3.3V it required more than 5.3V on input. LM7833 are cheap and provide more than enough current. You can try powering it from 2 AA batteries, but using external voltage regulator might be a better option. Voltage regulator inside usb to serial will not do.