aero affects grip the most, once your up to speed, but it also increases drag so you should try to get grip elsewhere first
camber will affect grip at all times and it comes without increased drag so I start here
toe doesn't affect grip in the same sense, all it does is give a faster response when you turn into a corner simply because the wheel on the side of the car taking all the cornering load is already pointing into the corner - it comes with increased tyre wear and should also sacrifice straight line speed
you can soften the front of the car, you will get more grip but it's less responsive (more bouncy) and you might have to increase ride height since the car could now bottom out
ride height should be low as possible, that way you get downforce from above, which unlike downforce from the front (wings) won't increase drag
key is to have it in balance, understeer might be caused by the rear not keeping up with the front so if you make a front setting change, you should change the rear as well if your trying to maintain balance