Is it necessary to use your modules to implement Doofinder?
No, it is not necessary. If you have a product data feed, e.g. Google Shopping; that's enough to get you started.
We couldn't check the plugin due to a connection error
Doofinder tries to check the plugin installation by a URL. If Doofinder cannot access the plugin, the guided configuration can continue. Just select the "other eCommerce" option as a platform and proceed with the configuration.