To Access Solmyr, the Academy Effret Hero, you will have to play as the Academy Faction and they are selectable as a recruitable hero.
To Access The Story of Solmyr and the Efreet Scenario Mission, select Single Player, and you will see the mission there.
To Access the Pre-Order Heroes, the Academy, Haven, Necro, and Stronghold factions each have an additional Hero. Each one can be recruited as a Hero in their own Faction.
To Access the Artifacts, they will be available for you in Ivan's Campaign. You can only access Ivan's Campaign once you have completed 2 of the 6 available campaigns.