Four-card feature solution on bare CSS flow - No Flex nor Grid

So, a few questions arised while working on this challenge:

1. What should be treated as first-heading (<h1>)? Some solutions made two headings for the first to blocks; is that right? What about accessibility issues?
2. I had a hard time figuring out the right proportions between fonts, blocks' boxes, margins, etc. in order to match the design previews. Are there ways or tools for that?
3. Finding a method for the making of the page also posed some problems. What should one do after defining the HTML and basic CSS (fonts, etc.)? What to tackle next? Are there known approaches to that? Just found myself iterating on changing things: markup - margins/padding - sizes - back on markup again...