Thanks for taking the time to visit the Community. I'd be glad to offer some info on your questions about inventory.
In the Simple Start version of QBO, you have the ability to enter products and services. The inventory feature is available in the Plus and Advanced versions of the software.
I've got an article for you that offers details on how to create and use a products and services list. You can check it out here: https://quickbooks.intuit.com/community/Help-Articles/How-to-create-and-use-a-products-and-services-....
Additionally, you may want to check out the plans available for QBO. This link will show you the options and the features included in each: https://quickbooks.intuit.com/pricing/.
If you have any other questions about the setup, please feel free to reach out to me here. Take care.