How it sounds to you is what matters. So while it seems large it could end up being the perfect size for you personally.
You should double and triple check for leaks. A sound deadener inside (not that foil back stuff). The last box i built i went cheap and just went to Pep Boys and bought some rubber undercoating to seal inside and for a tiny bit of deadening. I did a before and after test and noticed the difference. But i applied like 4 or 5 coats giving each coat a day to dry. Ya, i know a cheap alternative and maybe not the best. Wonder how many others have used this cheap method. Oh i also made sure the speaker binding post was already installed and wires connected to it as quite a few have mentioned this to be an area of leaks. So i sealed that from the inside as well. Only problem is it required the carpeting to be installed first. So ended up masking up the front of the box to not ruin the exterior carpet.