Most important fundamentals in your built/modded listening room?

Situation: We will be doing a basement renovation soon. At the moment, I don't have a full go-ahead to turn this room into a listening room. The room will be multipurpose for another 4 years (when the last kid goes to college). I am not working with $100k and an architect. This is about laying the groundwork for later adjustments.

Room:

• The room is a rectangle: 27 ft. x 17 ft. x 8 or 9 ft.
• (I say 8 or 9 foot ceilings because right now the rafters come down to 8 feet but the floor above is at 9 feet.)
• Walls are unfinished, the ceiling is unfinished.
• Two outside walls are concrete.
• The floor is concrete.

There's a lot of literature out there, including a great article by Harley about building a listening room. https://www.theabsolutesound.com/articles/building-a-listening-room

But for now, as I said, I'm looking for ways I can PRE-PLAN fundamental elements of the room so that later it can be tweaked even further.

QUESTION: What would you suggest should be done that is fundamental to the build out of the space?

• Wall construction?
• Dimension modification (cannot make ceilings higher)
• Electrical?
• Other things?

Thanks in advance for your tips!