Uston APC with I18; $5 minimum

I've played for a while with HiLo, decided to learn a more advanced count and chose Uston APC. I've practiced the count, and the I18,but won't visit casinos until much more practice--still takes me 30 seconds to count down a deck. How important is it to memorize the rest of the indices? Will going beyond the I18 give me a much greater advantage, or minuscule?
Second question : Where can I find DD with good penetration and $5 minimum (in US)? TIA