Interesting point. As both senatus as well as populus are masculine, and as word order is no guarantee, we cannot really tell for sure which word Romanus does indeed modify. It can modify senatus, or populus, or, as I tried to suggest: both. I don’t think Latin usage would necessarily require Romani in the plural to do this, albeit it is, of course, grammatically more correct.
My understanding is that attributive adjectives (like this case) generally (and correctly) agree in number with the nearest noun, while predicative adjectives would be plural when modifying more than one noun.
I think that “The Roman (Senate and People)” and “The Senate and the Roman People” are identical in latin, and thus technically ambiguous. We have the same problem in English, as illustrated here in the forum recently:
Not that an adjective can’t agree with the nearest noun anyways, but in this case the phrase “senatus populusque” is viewed as a joint entity. Hence a verb is also singular when this phrase is the subject.
Probably yes, since his official reason to march against Rome was to restore the People Tribunes rights. As Marco Anthony and other Tribune were expelled from senate when tried to veto the proclamation of Caesar as public enemy.
True and none Roman was better at it then Caesar.
I don’t know where but I did read somewhere that SPQR stood for Senatus Populus Quiritis Romanus and not for Populusque.