Hey!
To get that classic 'start with magic x' feel, you can use both the <skill: ID> and the <skills: ID;ID;ID> tags together on the same Materia item:
<skill: 10>: This acts as your 'instant equip' tag. The moment the player equips the Materia, they immediately have access to that spell.
<skills: 10;11;12>: This tag tells my plugin to track the AP progress for these skills. Since the first one (Skill 10) is already granted by the first tag, the menu will just show it as 'Mastered' or ready to go.