StemeduESP8266 ESP-01S WiFi Serial Transceiver Module with 1MB Flash?DIP-8 3-6V?Pack of 5PCS

Unable to get program to work. what settings when using arduino ide and usb to esp module? i can program other esp-01 modules ok, but these won't work

What is the Crystal Frequency of this unit?

Will this run reliably at 4.2 volts?

The description shows 3-6V, but those who have worked with these know they do not accept that range very well. What does that value describe?