As long as you have unique good content to share it shouldn't be a problem you can post upto 9/10. But if its repeat content then its better to...
Have a check on what 3rd party plugins/API services you are using and what data they collect. Whether the data is completely stored in your server...
Its good to check if the theme and the plugins have the updates to support the latest version of WordPress and update them all.
You can try pexels and for image size, use some online compression or change it to webp
Do we need to submit sites to search engines these days? I believe all of them crawl and get the site indexed whether we need it or not
Facebook has given comparatively good traffic for us. You can try some useful posts and it will slowly start delivering traffic to your site.
You can better try some good offer for few days to get orders and feedback, mentioning the offer is introductory and for the first few people....
Shouldn't be an issue as long as you are not planning any fraudulent selling or buying there.
Separate names with a comma.