So I am looking into it for the first point, I am indeed saving and applying the changes to my material.
I did test with emissive as base and unlit mode and it is closer to how it should look like, the other parameters are all default (opaque surface with a value of 0.8 roughness and 0.2 specular and no metalness and the rest is all default).
This is how it looks like :
Still a bit darker than it should be but at least it is not red. For the way i plug in the color i just used the color wheel and it gave me both the srgb and linear hex codes, when i copy the color, i pick the srbg hex code and it sets the linear alike by default (which is expected i think) and finally i have gamma correction preview on :
With gamma correction preview off :
But this is just for preview, from what i understood, UE doesnt work in the gamma corrected space, it does all processes in the linear space and the gamma correction is only applied by the monitor at the very end as necessary (like any other monitor) unlike Unity which gives you the option (unless in hdrp) to work on gamma corrected color values.