I like that you know the exact keyword you want to rank for. The good thing is that no matter the search engine, google or etsy it's still just a series software programs that is presenting results based on words people type into it to match the words in their database.
For etsy being relevant is matter of title, description and tags. Since your target keyword is wedding cake toppers your going to make that the first words in your title. Your keyword should also be int he first sentence of your description and located one more time in the first paragraph if it reads naturally with your content.
Your keyword should also be the first tag: "wedding cake toppers" plus other keywords you feel people would type to find your product.
Dirty little secret. The most popular youtube videos get millions of views. Savvy video makers who created similar type videos knew they could generate thousands of views by turning up on the side of the video. The suggested videos. To do that they would copy the tags word for word of the video getting the millions of views. There they would be right on side of that popular video.
Etsy is a different search engine than youtube but going down page one for the keyword you want to rank for and looking at every tag that's putting people on page one might generate results for relevancy. Obviously they've got it right.
For your own proof of things. Reverse engineer the first ten items for the keyword weeding cake toppers. Or any keyword you want to rank for. Look at the titles very closely, look at the price, look at the description, tags, style, materials, everything. Whether it matters or not. Soak in your competition.
Now look at the last 10 on page 250 or look at page 50 even. What's so special about the first 10 listings that they are considered relevant. When you spot the difference you'll be empowered to master relevancy.