I am a passionate clean coder leading by example from Switzerland. frightanic.com has been my digital home since 1997. I have been a committer with the NodeMCU firmware project since 2015. You can find me on Twitter, GitHub and Stack Overflow.
The data you enter in the build configurator is used to manipulate the firmware build configuration files accordingly. The firmware sources are then checked out from GitHub and built in the same environment with the same build scripts as used for the NodeMCU CI build. Chances are, therefore, fairly low that a problem you experience with NodeMCU on ESP8266 can be tracked down to a bug in my build service.
The heavy lifting is done by Travis, the awesome build guy. Travis, you rock!
This self-service build needs to stably run day-in and day-out 24/7. I do add new options from time to time if I can guarantee it doesn't add extra risk to the build process as a whole. Anything that adds a lot of complexity or risk won't make the cut.
Still, let me know what you dislike or what feature you're missing. Of course I'm more inclined to implement your feature if I remember your name from the generous donors list.
If you need more options you can very easily build the firmware on your own machine using my Docker NodeMCU Build image.
I can't tell you, sorry. Personally, I prefer to use break-out boards with on-board USB-to-serial converters. They allow you to simply connect the device to you computer using nothing but a standard USB cable. This also means you won't have to deal with any voltage conversion. The ESP8266 operates at 3.3V, remember! If you share my preference you might want to have a look at my NodeMCU development boards comparison.
The most likely cause is that the firmware is too large. You selected too many modules or fonts and/or enabled SSL, debug or FatFS. Make sure all options you don't really need are turned off.
There are two likely causes: the firmware wasn't correctly flashed or it's simply too large.
You may have selected too many modules and/or enabled SSL, debug or FatFS. It all depends on the runtime memory requirements of your firmware, your own code AND the type of ESP8266 module you use. Modern Espressif SDKs are so large that any NodeMCU firmware with more modules than my default set hardly ever fits onto older ESP8266 modules i.e. those with 512K RAM like ESP-01. There's a lot of info in the NodeMCU FAQ.
If it were easy to calculate whether your particular firmware fits your particular ESP a gauche would be available on this site. I dream that one day my users would pick which ESP8266 they use and I could tell them whether the firmware with the selected options fits or not.
The NodeMCU custom build service should be pretty self explanatory. If you're still stuck or want to report a problem then send an email to info at <this-domain> dot com. It's obvious that you stand a much better chance getting noticed if I remember your name from the "generous donors" list, nothing but fair.
However, you should note that this is strictly for issues related to the build service and not for issues with the firmware itself. If you need support for NodeMCU then turn to the NodeMCU documentation → support. Why? Because this is all free and with way over 1000 builds per week I can't do 1:1 support. Furthermore, if your question is public others will profit from the answers as well.
If you're convinced you found a bug in the firmware then please report it on GitHub.
You like none of those options? I'm also available for personal paid support.