Having a store without having a website can be hard, especially when you're not selling your own goods. You risk quality problems, unexpectant shipping fees, and having more product than you can move. However, if you plan out your FBA business you've primed yourself for success.
The choice of hiring a digital marketing agency or a freelancer is one that is important to your business. However, a freelancer can provide the same online marketing results as an agency can, usually at a lower price.
If you're serious about your marketing strategy and are not using YouTue video as part of your marketing mix you're missing out on a large percentage of potential customers.