According to the last image that you shared in "MS Office Online document editing in Web Application with documents stored in File System", it seems that a new Office Online Server farm was created failed on the local computer via "New-OfficeWebAppsFarm" command.
Please make suer the account has enough permission, for more, you could refer to "error while creating farm for Office web apps".
If you need to use the WOPI protocol to integrate Office Online and WOPI host, the related Microsoft documents I can find are intergration with SharePoint, Exchange and Lync Server, I haven't found any documents for integration with other programs for the time being. Thanks for your understanding.
Maybe you could refer to "Can WOPI server (Office Web Apps Server) be connected to Third party application?“.
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
Besides, you could also refer to "Example code".