Hi Amey! You've gotten some good advice here already. I just wanted to say that before you worry about memorization of facts, you may just want to do Singapore along with the hands-on math activities in the HOD guides. You more than likely may find that this is a powerful combination that is enough to produce proficiency with facts.
I just decided to pull out the math flashcards this past few days to see how my ds was doing with them (since we didn't do this during the past school year), and he did very well with them. That particular son of mine is pretty naturally good with numbers though, so it could be I'll be doing something more with my next sons!:o
But maybe, before adding more to your plate, you may just want to give what's written a whirl and add more if necessary - just a thought!
In Christ,
Julie