go to killerstrike.com for more information. He put a lot of information and discussion about different magic systems and the advantages and disadvantages about doing multipowers and VPPs.
While it's not pacifically listed in 6th edition (unlike 5th edition), I believe Steve said sometime in the Rules forums that it costs 5 points per OCV/DCV modifiers with change environment. If you went that way, you might want to verify that.