I would advise you to do PPC initially to get customers. But, make sure you use a squeeze page and opt-in form so that you capture the details of customers so that you can mail them again and again regarding various products. More importantly, PPC is good to determine whether the niche you chose is profitable and if people really do spend so much money buying products from that niche. If you spend too much time and money to do SEO on a site only later to find out that it is not profitable, that is gonna hurt you bad. I did it once, on my first site ever... 3 months of hard-work, several hundreds of dollars later I found out that the niche I chose was not profitable. That was a lesson hard-learned for me.
That is where PPC is really effective. Getting a surge of visitors for a short time and testing the profitability of your niche.