If you are running a HT you usually have room correction, so you shouldn’t have to worry about the speakers being too big, in terms of having too much bass.
With a simple room like that, check out AM Acoustics room mode simulator. Put in your room dimensions and it will help you not only visualize the room modes, but also help you keep your speakers and listening room away from the lowest modes.
My suspicion is you’ll have a few very strong modes in the lower 2 octaves and bass traps like GIK Soffit traps will really help cut and smooth that out.
The height of the room is rather small, so consider abosrbers in the ceiling between listener and speaker and/or below the beam you mention.