Not the best article but just my two cents…
Split CSS in more as one file is… Last year I was near by you but now… It’s easier to handle a large site with more as one or two css files. I use Sass and I’ve an Index file where I import all the partials and modules (settings, mixins, reset, base and so on). It works well.
I start with Sass and nesting was awesome :D I do it all the time and deeper and deeper but it’s not so cool. Now I use nesting but my target is to reduce it more and more. Stuff like :hover and :last-child and so on are great for nesting. But for all the other stuff I reduce it.
PX vs. EM/REM
I don’t unterstand where is the advantage to use EM/REM. Maybe for Font-Size it is a good alternative but margins and paddings? For me is a margin or a padding most of the time a fixed value that I choose considered and nothing where I said: Yeah, I increase the body font-size and all the stuff increase with it. No no, that’s not that what I want.
But thanks for your article :)