I'm in a similar situation but with a bigger room and more than enough mineral wood, 703 and foam
.
I think instead of 703 the whole room it will be safer to 703 half of the room per DanDan's advice and then fine tune by adding and taking from there and doing lots listening/recording tests.
Also, Ethan has been doing this for a long time and is older than all of us combined (kidding!
) so you might want to listen to his advice as well
