The problem with VIM is it isn't useful without lots of experience, and knowledge of its tricks. When you have a text editor that you can buy multiple books about, you know things aren't simple.
Notepad++ is cool, but, only useful for the Windows crowd.
In the '90s, I used to really like Super Notetab. Newer versions I liked less, and never really found something I liked as well.
I'm mostly using Gedit right now, but been toying with other stuff.
vim can become useful to you in a matter of hours. It took me a couple of days to be _completely comfortable_ with hjkl movement and basic hotkeys like
-$ to go to end of line
-^ to go to beginning of line
-/ for searching the file
-w for moving forward a "word" (i.e. block of text as separated by delimiters), and b for moving backward
-## to go to a line
-regex search and replace (<- caveat is that I had experience with regexes. uncaveat is that every search and replace uses regexes...)
-yank and paste
+ a few more I'm sure
They aren't tricks. The entire point of vim is to use hotkeys. It's not like it's a text editor and "oh yeah, you can use these cool hotkey tricks I added". It was built from the ground up with that intention.
You don't need textbooks to use vim. You will probably get everything you need via search engine queries like "how do i do [foo] in vim?". If you end up hacking .vim config files then you may need help at the IRC channel, but the documentation is actually amazing with great examples.
If you are going to code for a living, please dear god do not use editors without learning some hotkeys. Even if it's not vim, you should at least memorize hotkeys for things you do _on a minute basis_ while you are coding. It is beyond stupid watching someone spend 30 seconds typing something which you could do in <5... using only basic basic basic hotkeys (nothing special like "VS code snippets")
@OP I agree that HHKB is a silly recommendation for your first mechanical kb since it requires you to change your typing habits. If you could only buy one. Ever. Then maybe the leap is worth it. But I would say any decently made board would suit you. Mostly everyone is happy with browns and blues for typing. The youtube videos already posted give you a good indication of sound.