Just thought I'd chime in here, on that note. I recently had a very large, and very powerful army totally decimated by 3 Fires From Afar. It was very expensive, and demoralizing.
Also, oddly, I was just thinking the other night about indie priests given a Shroud at 7hp, for perpetual gem income with little/no micro.
If you were to somehow manage to start this up with Caelum, you could even use Seraphines, who are stealthy (hard to interfere with), and can stealth preach your border provinces while they farm gems for you. But 4N is a weird path for a Caelum pretender, and you'd have to work hard to get a fetish economy in most cases, so it would be rough. Others have stealthy priests of course, but not flying.
