[Endoperez]

That general strategy might work. You just have to come up with a way to start conquering provinces before you get to Conjuration 7 and Lamias. I think Carrion Woods can conquer provinces even without a combat pretender, especially with high-level nature blessing. You took expensive magic, and received a good blessing, so you could as well use it! (before the population of your capital withers away and you cannot recruit any more living units)

You might also want to use more cheaper mages instead of fewer good ones for research, as magic scale gives more benefit to more mages. You should also search all your conquered provinces for nature sites, to get more gems and researchers.