With this strategy, you need to use mages for fighting, even in early wars. You can't just hire Warlocks, they are too expensive, and you won't be able to keep them all alive. You need to hire Warlock Apprentices, and nearly all of them should be out expanding (including hunting if they are in a decent province and have run out of slaves). You need indy commanders to shuttle slaves back and forth, and to hold slaves so your Apprentice is only carrying 3 when he attacks an indy, because if he's holding more you'll lose them when he retreats.
And of course I was involved in an early war.
The first war I had was with Pan, around the end of year 1, which was horrible and not what I would have chosen. The Call Horror strategy really doesn't work well against harpy PD, so I could only attack with Salamander-infantry armies. I think I made a few fireball wands for indy commanders just because I couldn't hire enough mages in my capitol. We hit a stalemate on one front where we both had lots of PD, and then I broke through an elephant indy on the other side using Beast Trainers. Pan had already been weakened on that front by another fight.