By default AI is supposed to be able to outnumber you, that's why there's a reduced AI bonus option in the installer
As for the merc pools, I suspect they start full, what can be done is to slow down replenishment rates though.
I also think it's better to start with full mercenary pools. Some core factions start with some pretty tight battles on the first couple of rounds, like Rome, Epirus, Pontus and GCS. If mercenaries are not available from the start early game will be much more difficult for these factions.