Boosting on Instagram does help a lot. I checked your instagram and observed that you don't use hasgtags for your posts. Hashtags help you to reach out to your target audience organically. So apart from boosting, you can also try and use relevant hashtags for your posts. Research hashtag tool will help you.
Retargeting works in every form. It doesn't matter if it is a video or an image or set of images. As you already have pixel installed on your page, you can make a custom audience of people who visited your store and did some activity like add to cart. Using facebook ads to build list could be costly. You can generate content and drive traffic to your store organically. Retargeting your website visitors on facebook would be a better option. Check out these content ideas which can help you increase the engagement.