I would also recommend starting with White Mage. You have higher raw healing and damage outputs to help out as a beginner. Just remember to make use of the off globals that are free of mana cost to keep your mana up. Assize is your friend for countering unavoidable AoEs.

Since you leveled Summoner, Scholar should be levelled up the same being linked to Arcanist as well. When the group is going well with low damage taken, you can have your fairy "slave" do the healing while you DPS. The burst healing does require the use of the Aether resource, so it may be a bit more difficult than White Mage due to that.

Astrologian might be the more difficult pick to master. The healer spells are indeed more simple than White Mage, but proper card use takes some memorization of which one goes where and what seals they give.