Great questions! Granted, any work you choose to do to your site should be done on a local copy of WordPress or a staging site. It is bad form to make changes to the production site unless you are sure they will not affect user experience.

That being said, since this is a custom theme by a developer, you may wish to reach out to them in regards to changing what they have built, there may be strange dependencies built into the theme that you would need to consider.

Additionally, changing themes is easy with WordPress. If you make a local copy of your website you can experiment with new themes and make corrections to the layout without fear of messing up the production site. Then when you’re finished you can backup your current live site, then push the development copy to your live production server.

I highly recommend checking out WooCommerce, it’s a great marketplace plugin that you can build out with addons.

Hope this helps

Woocommerce offers a slew of extensions, and yes, themes. While most themes can be made to work, these themes are designed to work. Some themes offer additional features which can be useful. You should work with the WC features alone first to see if any additional needs develop. Then seek themes or plugins that will address those needs. If WC meets your needs alone, then you are free to use any theme that appeals to you and even switch to another if you want to at a later time.

If you depend on a particular theme feature, you become locked into that theme. Something to avoid if you can.