Locum Tenens after departure of a patriarch

qawe

So I was just thinking... After the departure of Pope Shenouda, it was very obvious that Met Mikhail was the most senior hierarch, and then Met Pachomious would come next, but what if it wasn't so obvious?

1) does the Locum Tenens have to be the most senior metropolitan, or may he be a diocesan bishop? What about a general bishop? Or a general metropolitan (if such a thing were invented)?
2) if he must be a metropolitan (or diocesan bishop), is seniority calculated from the date of ordination to the episcopate (which may be general), enthronement to a diocese or elevation to the metropolitanate?
3) what happens if there are two hierarchs with equal seniority? Who becomes locum Tenens then?
4) may a khoriepiscopos or a patriarchal vicar (a married priest) be the locum Tenens if they are the longest-standing member of the Holy Synod?

I know these are hard questions, but I wonder if someone here actually knows the answer!