Progression through Ars Magica is not required for the midgame, however it is unlocked in the midgame.
To start with the mod, you will need an Essence Refiner and an Arcane Compendium.
The Essence Refiner requires you to either have done bees to get scented paneling, or to have been to the Twilight Forest to get Knightmetal Ingots.
After this you can do Infusion Crafting to acquire your Crafting Altar, which you need to make spells.
To learn how things work in Ars Magica, you need an Arcane Compendium. To get this, simply find a pool of Liquid Etherium, and put a Book in an Item Frame near it.
This will make the Arcane Compendium, which will then allow you to learn all about the mod.