If you have 3rd party apps loading, then 30% isn't bad with the PSI tool. Most active ecommerce score low with that tool.
I would start with optimizing your theme as much as possible.
Then if you want your site to load faster you can look at integrating app functionality directly into your theme.
To analyze your site run it through the Shopify Analyzer - it's a free Shopify specific performance analysis tool my team built for the Shopify community.