I have a setup, with ESP-Link firmware on an ESP-01.
Power is UBEC -> 3DR Air radio, + power to a small adjustable $0.50 switching voltage regulator (also have LM3117-3.3V, but decided to use switching), which deliver 3.3V to ESP-01. Then a 1k resistor from 5V to EN_CH. To protect the input, I use a 1N4002 diode inline from TX of 3DR radio -> ESP-01, should drop voltage around 1.0V. Still not 3V, but should be fine.
Have it running with Mission Planner Windows, Tower on Android, and this software on my iPhone.