Hello,
Years ago I was in the same boat. I researched insulation for audio with rock wool. Try to leave a 2” gap between the Rockwool and the space above it. It is better than stuffing the whole space with the insulation. Please call the companies about a referral of what to get. As said above try not to have skyline defuse panels behind you if you are close. It sounds really weird. First reflection points first. You can try this out with a small blanket or towel pined on the wall. I love the idea of the bass traps but you are very limited do to room size. In most cases you are going to have the speakers on a short wall so you can get some space in the front and back. Otherwise you will be dealing with slap back from the rear wall. Since you are doing this from scratch I know their are ways to do some of this by actually using the wall and ceiling cavity. I know plywood is so expensive but I am thinking of doing a plywood room/ drilling holes and maybe using some carbon fill. Great for bass control. Then, worry about reflection points. I want to do the carbon fill in my room since I have a 12” raised platform for stadium seating. Just to let you know. After you get the room done you can control the rest with power cables. I would call Straightwire and get their recommendations for cables. One your room and gear is in. Anything you need to tweak or correct the sound they can help. Most people would be surprised by how good even their affordable lines cost. If you are doing subs please stick to sealed box with good brands like JL Audio, Rel, and a few others that are more specialized but are designed for two channel. I hope this and one of these acoustic companies can make your room great.