ALL these things are very important. Once you have corrected ALL these areas that effect starter motor performance you can also install a simple ignition power interupt toggle or pushbutton switch on the dash to allow you to disable the spark momentarily for hot starting. This removes the cranking load on the starter allowing you to crank over and purge the intake manifold of over heated over rich air fuel that will not burn.
This is why a hot motor needs to crank for a longer time to start.
Once a fresh air fuel mix is drawn to the intake manifold the motor will start instantly.
Kick it over 1- 2- 3 count and throw the switch. pretty simple.
Make sure the GM OEM rear starter motor bracket brace is installed. The two bolts alone are not enough to support the GM starter motor.
This is not a replacement for correcting the other issues grounding, heat shield etc.