Would you consider learning vim?

Folding solutions are built in.

Here is a solution for folding EnergyPlus objects

:set foldexpr=getline(v:lnum)=~'^\\s*$'&&getline(v:lnum+1)=~'\\S'?'<1':1

:set foldmethod=expr

To build equivalent folding solution to above you your would have to specify fold markers using '{{{' and '}}}' similar to the way you are using '#['

Then use:

:set foldmethod=marker

I regularly work on IDF files that are 50k+. Vim works well

Hopefully there is an Emacs guru here to share their folding solution.

Would you consider learning vim?

Folding solutions are built in.

Here is a solution for folding EnergyPlus objects

 
:set foldexpr=getline(v:lnum)=~'^\\s*$'&&getline(v:lnum+1)=~'\\S'?'<1':1
foldexpr=getline(v:lnum)=~'^\s*$'&&getline(v:lnum+1)=~'\S'?'<1':1
  
:set foldmethod=expr

To build equivalent folding solution to above your would have to specify fold markers using '{{{' and '}}}' similar to the way you are using '#['

Then use:

 
:set foldmethod=marker

I regularly work on IDF files that are 50k+. Vim works well

Hopefully there is an Emacs guru here to share their folding solution.