Here is what I'd go with if I wanted to do a buffer charmer. (Bonus, you can have a cool harp for the RP aspect)
Stats
Presence, Willpower, Agility. More Presence will boost your Leadership score (passively buffing your allies and summons), Willpower will help making some of your powers stronger (affecting magic damages, healing and some buffs - just note that Song of Courage is based on Presence), Agility is there since you generaly want to be amongst the first to act (to throw your buffs around as soon as possible, nothing more anoying than having your whole party act before you can buff them) and it adds some boost to your defenses while allowing your offensive powers to hit their target (more important if you go with Aria and Dawnbreak, tho)
Arguably, you can trade Agility for something else if you pick other options instead of the two offensive powers bellow (like going for Group Heal and a Summon instead)
Powers
At-Will: Song of Courage (before lvl4, you can go with Bolstering Dance)
Recharge: Blessing (especially good when you get Expert Inspiration at lvl7) and Aria of the Waves (You'll want the Harp for the leadership bonus and the spell has a minor secondary effect affected by Expert Inspiration) or Group Heal.
Encounter: Dawnbreak (before getting it you could go with a Summon, that would be one more character benefiting from your high Leadership score and buffs).
Ultimate: Unbreakable (if you feel squishy or are often targeted. Bonus: it synergize well with Expert Inspiration) or Inspiration.
Gear
Anything that gives leadership, next to that Initiative is pretty nice, but also rare, Spell power is also important. Crown of Winter for Dawnbreak, Harp of the Waves for Aria of the Waves.
Companions
With the above build, I'd go with a weapon based DPS as a companion (to benefit from the weapon buffs from Dawnbreak), AoE powers like Cleave are also welcome. Brint/Brienne, Arona, Azyrran all have at least one set with Cleave, for instance. Etheryn can be a good second companion (buff to your initiative, weapon dps and a bit of healing in her Outrider set).