As a homeschooler, I would not hesitate to begin Level B in the middle of the year. That's the nice thing about doing it at home, right? You can go at your child's pace.

The starter kit includes all the cards you need for math games in your level. The "math card games book", is separate, but no worries (You won't need that book until level C, I think). In Level B, when a game is suggested, it includes instructions for how to play it.

I hope this helps!