Alk between 7-8 dKH is ideal. If you are at 7.5 that is perfect. Key is to keep your Alk consistant without any big swings.
Ca 400-450ppm. 420 is perfect.
Tailored Aquatics supplements can get expensive over the long term. Alot of people use DIY supplements such as simple baking soda to maintain Alk and cheap calcium chloride (there is a sponser on Canreef that many people use).
Good article is -
http://www.reefkeeping.com/issues/2006-02/rhf/index.php
Tons of good articles in the Canreef reference library (at the bottom of the forums) on chemistry, Alkalinity and Calcium.