When you want to use the EQ window, try this. Load the house curve for the overall shape that you want to use. My spreadsheet will create a file that is named "REW_Curve_something_overall.txt". Use that one in the REW house curve selection.
Then go to the EQ page within REW and try these settings:
-target settings
-target type, speaker driver
-crossover HP cutoff (Hz), 80
-crossover HP type, LR4
-crossover LP cutoff (HZ), 300
-crossover LP type, LR4
This should create a target for your midbass speakers. Then adjust the highpass and lowpass type and frequency to adjust the target for your subwoofer and your dash speakers. This is a very similar process to using the individual text files that the spreadsheet creates, but it takes a little less clicking. Thanks to jdunkl and others who helped discover this trick.
I cannot help you much with the auto eq settings like filter tasks, match range, max boost, etc. I do not use the auto feature and don't have much intuition with what settings work well. I strongly encourage you to try creating filters yourself, if you are comfortable trying it. Just keep the Q values around 0.5 to 3.0 and you'll avoid chasing your tail too much.