No thinking involved at all outside of your normal design method. No need to investigate the latest trends or activities by some online guy. Just do what you do.
"Just". What I remember from that time was putting a button at relative 0,0 and it being at the top-left of the page in one browser, but was offset in another because that browser was adding padding/margin to <body>. I cannot say which was "correct" but it nonetheless pushed me to use normalisers, which prevented this kind of problem from ever coming up again.
No, a browser's defaults are, well, its defaults. One doesn't reset to them.
I think the line between a normalizer and reset stylesheet is _very_ fine, if there even is a line. A normalizer is probably _slightly_ more opinionated than a reset stylesheet. In the end, the difference isn't really important. If you need a reset stylesheet, normalizer will probably do just as well.