Your main Sov doesn't have an Int requirement on any spells, so as long as he is the one casting the spell, you're good to go. On top of that, you need to have access to each of the elemental shards in the game. At least one fire, earth, air and water shard in your control.
As for mana, the trait is a great way to start, but you'll want to snag every shard you can, then upgrade those shards to Greater Shards whenever you can. For the Kingdom, there is Shard Mastery tech after Shard Harvesting, that bumps the shards to Greater Shards, which gives you an additional 1 mana per shard, plus gives you the option to build a Temple of Essence which adds 3 more mana to your pool. You'll have to connect your settlement to the shard itself in order to build the Temple of Essence though, the shard needs to be within your walls. Mathematically, that means each settlement connected to a Greater Shard with a Temple of Essence can produce 6 mana per turn.
