Hi there,
First thing I would do in your situation after being open for a year and a half is look at the data I do have - who have been your customers? What age range, gender, country etc etc do these people live in - that would be the first thing to check to see if there is a pattern that you can utilise.
In regards to the website it looks great. I really like your logo, it works well with the products you sell. First things first, retain the interest of the customers that you DO HAVE going to the website - With the announcement bar I can see you have put a long tail keyword in there with a link which is great for SEO, but you also want to get a customers attention to click on that banner - if for anything to keep your bounce rate down. What I would do is put something like ’ Free Delivery On All Of Our Premium Coffee And Artisan Products’ or if you don’t offer free delivery put something like ’ Find Out More About The Story Of Our Premium Coffee And Artisan Products’ - just something that adds a bit of intrigue to get them to click.
I would possibly keep your slide show down to 2 images on the main page - I have seen a lot of videos recently about website owners finding that revolving slide shows dont actually convert any more - I am not sure how true this is so I wouldn’t say change this but you can always mess around and see if this impacts you at all?
I think its great you have a blog but to someone who has only just come onto your site you dont want them to think your site is just for information about coffee etc so I would move this section to the bottom of the page and put your collections at the top under the banner. You could put ‘best sellers’ or ‘new products just in’. I would also say that the product testimonials should be almost center on the page and this should be highlighted as it definitely adds trust to your brand.
In regards to SEO there are 2 parts to look at. For a start your ‘on page’ seo. On page SEO will include; images, titles, description and meta information. I was always told by someone that you should write your product pages like you were writing a newspaper. So you should have a main title (the H1 tag) which is the one shopify will generate for you. You then can add your own h2,h3 and h4 tags. For example:
Hi, my name is Emma and I own BBQ BOX UK
My store is only new too but I have created websites for years and have had success with a lot of them during this time. My problem is that I become bored when waiting for SEO to take effect and then become excited by a new idea (my bad).
If you take a look at bbqboxuk.com you can see our story as to why I have chosen to stick with this product niche - since I am just demonstrating on page SEO I wont bore you with that 
I hope I have helped you understand this a little better by writing this out this way. I am in no way an expert, I have just always enjoyed SEO and how to achieve it - unfortunately it will take you a few months to get going while the search engines process this. That said your domain is 18 months old now so you may find it quicker compared to a new site as google with look more favourably at an aged domain.
So the above would be my example of on page SEO. You can see that the header is a H2 and then respectively there is a H3 and H4 tag. Each heading has a keyword in it which I have highlighted and linked to the respective page. In my opinion in these headings you should only link to your own site - you dont want to really link to a third party site as this will take the customer away from your own site (and we want them to stay on the page and buy) - the only way I would add a 3rd party site is if (a) I owned or was affiliated with that site or (b) if it was a market place where I have a shop for example Ebay. You can always make your prices cheaper on your website compare to the Ebay store to hopefully show trust but then regain the conversion on your website. Lastly for on page seo make sure all of your images have your keywords in the alt tags - to do this click on the image and type the keyword into the text bar in there.
Other SEO techniques for off page are to gain backlinks for priority sites that give you a ‘do follow’ link back to your website. For example if we look at shopifys example sites; Shopify Ecommerce Store Examples you can see that each of them have a link to their site. As shopify will have a high domain score this will in turn be seen (in the eyes of a search engine) that the site it is linking to also has a high domain score (as they trust shopify not to link to spam sites).
So you need to look for sites where you can get a back link of this quality. A good way to find these is going to Ebay and doing an about me page and adding your website link in there. You can do this with most online market places also. You can also look at blogs and news sites that allow you to do your own press releases. Now you will need to write between 1,500 to 2000 words to get good traction on this however it is doable and doesn’t cost a lot to do.
Another good and cheaper way to get traffic is to go on youtube - you should have your own channel and show your products in videos - you could make some really cool videos about where these products come from. For example; I follow this guy Elliot Prendy (no way associated with him), if you look at this video he made its a perfect example of how to get traffic; The Best FREE Traffic Methods for Shopify Dropshipping - YouTube - look for the part in the video were he talks about the Japanese Vase that he was selling and the video he made on youtube - it is a real eye opener on how to get traffic for free.
Lastly in regards to paid for ads, google and facebook are very expensive - bing shopping can be a little cheaper if you go on bing shopping - I am not sure if you have Toboola in your country but these are by far the cheapest ppc and they offer great help.
I hope that this helps - I am in no way an expert - these are only parts I have picked up whilst trying to do my own website…