So if I've got this correct.. DataBridge v2 will give me back server behaviour panels - so my historical reason for not upgrading to the latest DW cc version can now be forgotten.
In order to connect to php7.3 regardless of what version of DW used (2014 or latest), I need DataBridge v2, as somewhere in the coding there is updated php7.3 compatibility. DW & DB v1 are just not capable of connecting to php7.3.
And your No 1 recommendation would be to upgrade both DW and WA-DB if I want to use the latest php version
I don't think the connection problems is with the testing server settings, because when I change the database to php5.3 it connects.
In testing the DW connections I have experimented using every combination for the testing server settings
http://www.domainname.co.uk http://domainname.co.uk https://www.domainname.co.uk https://domainname.co.uk
When using php5.3 all 4 combinations connect, but using php7.3 all four give the module not installed error message in DW.
Also as part of my overhaul of my sites I have also installed ssl certificates (Let's Encript), all done within the Plesk environment which allow me to set 301 http to https redirects. Again I have tested the 4 http/https/www options with and without the ssl/301 redirects in place.