[Endoperez]

That is what you would like to do, but what if you never find any earth sites? Or any astral sites besides your starting one? Those things do affect your strategy. Think about things you will do if things don't go as you want them to go. Oh, and Acashic Record is quite an expensive spell: don't use it just because you can. Astral gems have better uses. (I do the same thing myself all the time in Dom1, and am finding out why I shouldn't in my current game...) Conjuration also gives you Angelic Hosts, Harbringers and Coatls, all are very nice summons. And depending on the gem income you get, you might be able to summon various elemental courts. With some items, you can go for Air you have your own mages, Fire you can get with Archangel from the Host, Water has cheap bonus items so you might be able to get them too and Earth might be possible with your pretender and some of the more expensive items (elemental staff and ring os wizardry).
What level of Earth does Firbolg Fortress need? If it is three, you might go for that. The free forts help, and that must be the most common castle-giving site in the game. Atleast it was in Dom1...

Okay, there were some thoughts. Not sure about its quality, but that is the advice I can give for you.