Number properties is an important topic, so go through the general chapters carefully right now, but save the advanced chapters for a bit later. In general, go through the general chapters of all 5 books, then come back for review and add in the advanced chapters in your areas of strength.
Also, I just wrote an article that compiles a bunch of previous articles I've written on NP. I must've been reading your mind. :)
Go onto www.beatthegmat.com
tomorrow and look for my article - it'll be at the top of the homepage. I do recommend that people read / do the general chapters first before digging into that article. It sounds like you've already done that, but just FYI. I'd do general chapters, then use this article to start to introduce yourself to the trickier and more advanced aspects, then go to the advanced chapters (or do a mix of the latter two).