Any way to open files with your default programs in MC?
Is there? There is. It's in the documentation somewhere I swear. I just never bothered doing it and just open stuff by invoking the program through the command line.
Notepad++ is pretty popular it seems. Most of the people I knew who used windows used it for coding in anything they didn't have an IDE for, or used it for everything if they didn't like IDEs at all. Me included.
What are the benefits of using Vim or Emacs over other similar programs?
The biggest benefit of vim is that quitting it is so hard you'll only ever want to do it once and then never go back.
As for emacs, the most general advantage is that you can do absolutely everything you need through the keyboard without leaving the touch-typing position(some modes break that rule, but you can just reconfigure their keybindings to something more comfortable) and efficiently at that. It takes a big learning time and constant practice, but it really makes a difference not having to take one of your hands out of the keyboard to click on menus or browse your code/text.
Then there's just how customizable it is. It's just a small C core with everything else in elisp and mostly fully exposed to the user. That, the big community and the ability to tack individual minor modes to any major mode make for endless customization.
Apart from that I'm quite fond of how the buffer system works and orgmode alone makes it worth giving emacs a try.