In my Julii game, I was around 40 cities and having no trouble from the Senate. So I am not sure 30 is a magic number. I did all the Senate missions and they were as happy with me as with the other factions with much less territory. I don't know how long I could have kept going - but I suspect I could have taken 49 non-Roman cities and then ended the game by taking Rome without a prolonged civil war. I decided to start the war when the Senate wanted me to attack Egypt - knowing civil war had to come for me to win the game, I thought starting it when my enemies to-be were fighting the powerful Egyptians was as good timing as any.

BTW, does anyone feel a bit sad having to make a bid for Emperor? I would have liked an option to win by upholding the Republic (a much more attractive concept)!