1. If you have a standard WordPress with WooCommerce installation then WooCommerce will insert the Google Analytics tag on all pages. I suggest to give it a quick try (disable Yoast Google Analytics, enable WooCommerce Analytics and e-commerce tracking). Check if it is working with the Google Tag Assistant browser plugin. If you use some sort of caching mechanism, make sure to delete the cache before checking the tags.
2. My plugin dynamic retargeting plugin requires also to have a Google Merchant Account up and running. If you have one for your shop then installing my plugin will suffice. You can delete the old retargeting tag. Again, make sure to check everything with Google Tag Assistant.
If you run into any problems, please give me feedback. It will enable me to write a better setup guide for my plugins.