ok, I'm far from an expert on this, so take my suggestion with that in mind.
I went through those videos as well when first doing eq, and tried REW's auto eq functions. But after a while, what I settled on these days, is a way simplified approach.
Assuming you already have the cal file set up. Use the 90 degree one, as you'll be pointing the mic upwards.
1. Click the Measure button in REW. Beside the Output dropdown, set to either L or R, so that you only measure 1 channel.
2. Sit where you normally sit, hold up the mic somewhere in front (3-5 inches) of your face, with the mic roughly at ear level, pointing up. Then run the measurement. You now have 1 measurement.
3. Do the same for the other channel.
4. Now click on the 'All SPL' tab above the graphs to see both left and right channel. You should be able to compare the 2 graphs. Start by focusing only on the 100-200hz region.
5. Now, instead of using REW's auto eq, try using APO to knock down any of the massive peaks you see, manually. Using the Peace UI addon will help a lot here. Probably focus on 1 channel first.
6. Then run the measurements again to see how your eq affected the result.
7. Rinse and repeat. You'll probably be playing a lot with the amplitude and Q factor to get the frequencies to behave and at the same not affect the surrounding frequencies too much.
In this way, you're getting your hands dirty, you're getting quick feedback on how your eq affects the measurements, and focusing on the area below 200hz makes it easier for you to visualize the results (you can move on to eq higher frequencies if you so wish later).
While holding your mic in your face is probably frowned upon by purists, as long as you hold your mic somewhat still, the measurements (for lower and mid frequencies) should not deviate too much (can repeat a few measurements to compare). And note that our bodies make a measureable difference to the results. Also, it's way faster than having to crouch beside your chair while trying to click the mouse button. You can try various scenarios later to see the effects on the measurements (your body in chair, mic in your chair and so on).
If both your left or right channels are already pretty close in measurements (and your room is not affecting any single one of them weirdly), then go ahead to measure and eq the L+R. To be clear, after going through the different methods of measurements, nowadays I just tackle the biggest offending resonant frequencies and call it a day...
But that's just lazy me....
And from your posted graphs so far, it does seem that you should be getting a sub instead for the biggest gains...