Would it be helpful to move the additional help sources to the extensions page (and rename it to "Add-ins")?
Just throwing ideas out there, we could also add an "Advanced" tab where we put the settings we (really) don't want others changing without good reason (such as the indentation width). However, such a tab could quite possibly mean reorganising the entire settings dialog.
While the original intention of this issue wasn't for a complete reorganisation of the dialog, I am more than willing to spend some time if we want to tie several other issues into this one (and it would be helpful to do so).
Another random idea is to copy other IDEs and use a tree on the left-side to navigate to different settings, which would allow us to keep the number of settings on a page much lower.
I will write a new prototype trying the "Shell/Ed" tab idea you suggested and will upload the relevant screenshots.