Ideal Listening room

I have the opportunity to finish a second floor level walk-in attic space over my garage from scratch. The space when finished will be 11 feet wide if I use a 5 foot knee wall, or 13 feet wide for a 4 foot knee wall. The room length is 18 feet. The ceiling height will be 7ft 6 in if I panel the existing collar ties to create a flat ceiling in the center of the room. The center flat section is about 6 feet wide. I have no clue as to the acoustics of such a space. Another option is to paint the collar ties and panel the cathedral ceiling above which reaches a height of 9 ft 8 inches at the apex. I obviously need professional help. I am concerned about the size of the room and issues with low end nodes. I may use Reeves for assistance regarding building materials and room treatments but is there another consulting group so that I will have two opinions??

Any comments about the overall acoustics of sloping attic walls?

Would you place the speakers facing the long or short dimension?

Is the narrow width of this room and low ceiling a problem?

If I put the speakers facing the long dimension, then at 7 feet apart, they will only be off the vertical knee side walls by around 1-2 feet. Is this enough?
Will low end resonance be a big issue?