Some of your questions might be answered at www.kriegerbarrels.com
Go to FAQ/proper reloading practices.
I consider this to be the expert source.
I don't disagree with any of the commentary or recommendations in that article from Krieger barrels; it is consistent with information you would find in any good reloading manual. However, using your own chamber and adjusting your dies accordingly works very well in the vast majority of reloading situations. If someone wants to make the process more complicated or expensive, so they KNOW their chamber, there are tools for that job. As long as I'm still getting very accurate and safe ammunition, using simpler time-honored methods, I probably won't change how I've been doing it for almost 30 years.