My idea would be rather to attack using a priority target system, work out which cities are:
a: The weakest defended? Attacking the weakest cities first allows to destroy Caesar's capability to retaliate much faster.
b: Which cities are most valuable to us? Which cities will provide the largest return, the fastest, on our investment of hammers and gold into them? These cities obviously need to be considered higher priority because they create the least stress on our already fragile economy.
c: The least important category honestly, particularly seeing as how we're protective. Which cities are the easiest for us to defend against counter attacks? As soon as we get Longbows, as Churchill, this category becomes nearly irrelevant but given that our economy is straining our research might drop to low enough that we may be without them for some time and as such it needs to be considered.
Hope that clears it all up for you.
EDIT: The Germans should accept it as long as they share borders/have cultural influence in it if I remember correctly. It's been a while since I played regular BTS so I'm not entirely sure.