I just finished my basement room a few weeks ago. I was in the same situation as you with not knowing the best way to build the room but wanted to do it right to achieve the best sound I could. I ended up going with an acoustician to design the room for me and I built it. His price was VERY reasonable. I recommend consulting a professional to at least get their thoughts. Jeff at hdacoustics is great to work with He I’d very thorough and knowledgeable. Good luck!
Ron