Complex sentence: Rainbow's first substantial expansion, in 1978, was the opening of a general store (selling vitamins, dry goods, housewares, books, clothing etc.) a few doors down from the grocery store.
Split into simpler sentences: Rainbow's first substantial expansion, in 1978, was the opening of a general store (selling vitamins, dry goods, housewares, books, clothing etc.). It was located a few doors down from the grocery store.