Since I last posted, I took a detour and played a full campaign on Caesar's side. This turned out to be surprisingly easy. I defeated Pompey fairly early on in Greece, and he died near Patras about 35 turns into the campaign. After that, I played until turn 59 (October 45) before I achieved a full victory, as the morale of the Pompeians had been shattered. I never quite defeated them in Spain, where a final objective city (Salamantica) still remained to be captured, but in the East, I won victory after victory. Defeating Pontus (again, with surprising ease) seems to have tipped the balance completely in my favour. I only needed to advance as far as Tarsus before the victory screen popped up.
At the same time, I continued my campaign on Pompey's side, but this was a total failure. I did go East and made some allies and raised some funds. However, the troops provided by my allies proved to be fatally weak (or I mismanaged them), and my Roman legions were too few to hold Greece and Minor Asia. I initially did manage to stall the Caesarian armies in Spain, but ultimately found myself overpowered there as well. The Caesarians just seemed superior in terms of troop numbers and recruitment capacity, while their generals were not any worse than mine.
Now I would like to try another campaign, playing Pompey. I have gained some ideas from the earlier posts in this threat, but I wonder if anyone has any further suggestions for winning strategies. I particular, I am interested in how to make more of the non-Roman troops provided by the Roman client states in the East.