Wow this discussion has moved faster than I thought it would. To address some of what's been said
I'm not particularly attached to the term "Prytaneion" and would be fine with "Cabinet" or the like.
As Al' Khem suggested, instead of having a broader "Cabinet" of vague deputies we could instead explicitly limit the assistant positions the Delegate can appoint to citizen-diplomats to assist them in their foreign policy role, which I think is likely to be their main responsibility and the one which is most difficult to do alone.
Whatever appointments the Delegate makes, I don't think they need to be approved by the Ecclesia. The Delegate already has the mandate of a majority in the Ecclesia, and I think to keep things simple and straightforward we should follow a parliamentary model like the countries Funkadelia cited rather than a presidential one. This has always been the basis we've worked on with executive appointments in the past and it's never been a problem.
I would be fine with including the community building aspect of the delegate's job in their explicitly enumerated powers.
I do agree that the Ecclesia should be the supreme body and that the Delegate should serve it rather than lead it.