It offers a good balance between protection and not cutting the drive voltage down too much. Mainly from imperial experiments.Powering from both sides is always preferable if possible.You should always have the resistor the 5V side of the of the converter.I am not convinced that those I2C converters are fast enough for Neopixel driving.
How.can I see if they are fast enough?
If the standard example sketches for FastLED or Neopixel libraries run normally, and the patterns and colours displayed are as expected, then the converter is fast enough.These converter modules are designed for use with i2C and similar signals, which have a data rate of 100KHz or perhaps 400KHz. WS2812B leds use a data rate of 800KHz. I found that when I used these adaptors for LED strip purposes, the strips displayed colours and patterns correctly, but if I touched certain contacts on the adaptor with my fingers, the strips would flicker, freeze and not show the correct colours & patterns. As soon as I removed my fingers, the patterns would return to normal. This indicated that the signal to the strip was only just good enough. Mike suggested that I should try a 74hc14 chip instead of the adaptor, and I found this was much more stable, because it did not react in any way to being touched - the colours and patterns remained stable.
because ambilight sends a signal every 15ms so it doesn't need fast response?
monitor blink black and then return the image
If I connect the power to the strip, and than connect the ESP to the PC, monitor blink black and then return the image.
I do not know what could cause that. I am also concerned that the pc could be damaged.Search your circuit for any possible short circuit. It may be that a short circuit could be causing to much current to be drawn from the usb port.
Yes, that is safe. Be sure to connect the GNDs together.
But if it's safe why monitor blink when I connect the esp to the usb?
Once you tell us exactly what you mean by monitor blink we would stand a chance of telling you. But as far as I am concerned your explanations are not very good.