I haven't attempted any such complete integration of NotePad++ with the Arduino framework. My approach was to use the IDE's File > Preferences > Use external editor feature, then use NotePad++ solely as an editor, still using the IDE for compiling, uploading, installing libraries, and installing boards. What I found I was missing was to be able to format my code to the standard Auto Format style. I'll share the solution I found for that (some years ago, so possible there are small updates needed):
Everyone has their preference of formatting style but my opinion is that what's important is to set a standard and use it consistently. The Arduino IDE has set a formatting standard with the configuration of Tools > Auto Format . I use this on all my sketches but I also want to use this formatting standard in my library and bootloader source files which I frequently edit with Notepad++ so I decided to add Arduino IDE style auto formatting:
Check the console output to see if the commands were run successfully. You can edit the commands by Plugins > NppExec > Execute...
Plugins > NppExec > Advanced Options... > Associated script: Arduino Auto Format > Add/Modify > Place to the Macros submenu(check) > OK > OK
To set the same shortcut key for Auto Format: Macros > Modify Shortcut/Delete Macro... > Plugin commands > Arduino Auto Format > Shortcut > Ctrl + T > OK > Close
After doing an Arduino Auto Format you can't use Edit > Undo to revert the change but if you're using the first Auto Format commands, which saves the backup file, you can add the option to undo the auto format:
Plugins > NppExec > Execute... > select "" from the dropdown menu