What assumptions do the articles make about the previous level of understanding of physics that the reader has? Also, I'm a bit lost and find the articles not so "clear" when I just jump in to read a random one - is there a suggested learning path or sequence to read the articles in where they sequentially build up knowledge?

Physics outlined on this site will be clear to those who already understand it at a reasonably high level. As MrCoffee implies, unless the reader has a "previous" understanding of physics—that is, the necessary and prerequisite knowledge of physics at an advanced (and broad) level—then much of these notes will not only be unclear but also hard going (thus likely not very helpful).

That said, concerning Units in Electrodynamics, ID: 00669, I wish I'd had this succinct (and for me clear) summary when I was learning this stuff, it's very good. (From my observation, units not only 'color' the way one learns this subject but also they alter one's perception or interpretation it (perhaps more so than in other branches of physics). Thus being able to move quickly and seamlessly between the different units ought to be a definite advantage.)