Creatives for few products(not the entire store) is better to start with. Facebook marketing can be tricky if you don't niche down your customer segments. You can easily burn your pockets if the ads are not targeting your customer audience. If you already have customer emails (or) leads i would suggest to try out this app(there's a free credit on it) to get your customer interests https://apps.shopify.com/customer-insights. Once you know your customer interests then you can segment them appropriately on facebook ad campaign or send them correct set of emails. This can help you to target similar audience too.