jenkinsci-users group is a useful communication utility, but it's hard to continuously monitor all messages there. In general I would recommend to ask such questions using Jenkins IRC channel or Ownerhip Plugin Wiki Page.
> What I struggle to understand is why I need to do step 1 and 2, and not only 3 to give the members of a group access to edit the job configuration and run it.
Ownership plugin does not have it's own security engine. It depends on Role Strategy Plugin. In role strategy macros are being used to register roles with special hooks, which then call routines in Ownership plugin on-demand.
Such implementation allows to keep both plugins independent, but it requires some configuration (which may be automated BTW).
> The access rights I set in step 3 would indicate that the users of the group could delete the Job, but I guess that's limited to the Project Roles I defined in step 1, correct?
Yes, the access will be limited to permissions registered for Ownership macros.
Currently, there's no filtering of permission tables. I'm not sure if it is possible to add such functionality w/o a full check of roles (multiple expression matches, custom macros, etc.). Created JENKINS-26397 for the case.
Hello, as there is no status update on this ticket, I take it that this feature is still not implemented?