Here are some answers for you that I believe will help you.
1. You should implement a long term and short term strategy right at the beginning. What I mean is that there are essential parts to your marketing like SEO and content marketing that you need to implement right in the beginning, but will take a while to filter through, but these are essential if you want to have organic traffic. That would be L-T.
The best for Short term for a newly launched site is ad's. Word of warning though. Know your customers demographics such as age, income, education etc, know your competitors demographics and then find the platform (such as social media channels) where your ideal customer is based on those researched demographics and then roll out targeted ad's for them.
2. You have to implement social media strategies right from the beginning of course, based on your demographic research.
3. Get busy Blogging - start with content marketing now.
4. Sweepstakes - start a giveaway to get traction with clients and create awareness.
5. Make sure you collect emails as these are like gold dust for future email marketing.
6. Video marketing is essential for competitive retail space and very powerful to get found on search engines like Google.
Prior to me launching my digital marketing business 5 years ago, I built an online retail business and made many expensive mistakes. And they can be costly if not implemented correctly from the beginning.
So in summary: SEO - very important, Ad's, Social Media, Sweepstakes, Blogging, Video & email marketing.
I trust this will assist you. Let me know if you wish to have a call to discuss these or have follow up questions.