It is always good to get the best understanding of suspension design you possibly can. No doubt about that. JMcdonough has a couple of good reference recommendations. To your questions about SAI vs wheel/tire width there isn't much you can do w/o major modifications to suspension parts. I have always run the widest wheel/tire I could figuring that the added traction will be great to have so I decided to put up w/ any side effects. Look at the first diagram here.
https://www.freeasestudyguides.com/included-angle.html
As you can see SAI is built into the spindle. In a standard short arm/long arm suspension w/ a large enough diameter wheel, you can ad wheel width both to the inside and the outside. As you have found out, a strut setup limits how much width you can ad to the inside of the wheel. But even w/o a strut, width added to the inside is limited by frame rails and or control arms since at full steering lock the rim/tire will hit them. BTW the scrub radius JM mentioned is the distance between the two bold dashed lines at the ground. You can definitely feel the effect if that radius gets too large. The whole wheel/tire/spindle assembly pivots around the point where the SAI line hits the ground. But outside forces (bumps, road slope, braking) will push the wheel at the point where the camber line hits the ground. So if the two points are further apart, the wheel gets pushed around more forcefully.