This is a more complicated pattern than any where I've used crossed stitches or fp or bp stitches. There may be other people who will see this who are more current on their crochet skills; since I started knitting a little over 2 yrs. ago I've hardly crocheted at all. All those post stitches...just thinking about them makes my hands hurt. I think you'll be glad you stuck with it and figured it out. Too often I figured out crochet patterns by frogging and redoing because at the end of the row I had too many or too few stitches. Enjoy! and I'd love to see a picture when you're done, if you want to post pictures of your WIP that would be great too. If you run into trouble a picture of the troublesome part sometimes helps.
I should never overestimate my basic arithmetic skills.