"The room can totally wreck, or make, a system"

The environment is always the first thing to fix, better yet design, correctly and then use room treatments.

Then it comes to placement of all the gear and furnishings, speaker placement most critical.

If the above are truly optimized then there should  be little or no need to equalize

If one must then always best to reduce levels next to dips, not add to the dips.

Next up is equipment, last on the list.

I have set up outstanding high end systems in a properly setup environment then dialed it all in, swapped to a system costing 10% and it was still dang fine and better than most super high end systems I have ever heard.

Rick

Design, including how the space is built, solid, laid out well, etc do the best you can then work around the other uses of the space. This will determine where the speakers are going to be generally located so pretty easy to sort out where the main treatments will be needed the most. The better the design of the space, the easier everything else will be.

If a room is to far compromised then all the treatments one could do might not be enough. I have listened to very high end systems I had to walk away from they sounded so bad yet I have enjoyed simple but well sorted systems what were a joy to listen to.

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40 hz null pretty tough to deal with

90 hz peak, I would look into a trap(s) tuned for 90 hz

Peaks are far worse to listen to than nulls and often easier to fix.