A few fun tips:
If you wait until you can summon a black servant, you can prophetize him for a cheap H3 undead to reanimate tomb wyrms.
If you take some sort of bless the priests can become decent thugs - good HP, natural prot, 0 enc, self bless. Best of all, you don't need research to summon them.
Poison slingers firing over your skeletons can do a lot of damage without worries about friendly fire.
LA C'tis has a hero with level 5 holy magic
You actually do have nature and astral magic: empoisoner has N1, and Sauromancers get astral randoms. If you can summon it (with your pretender or indies), the Couatl gives you level 3 of each.