I can second the Bard suggestion. I have most of my versions of Astarion run around as Rogue/Bard multiclasses and it is extremely satisfying. 4 Rogue(Thief) and the rest School of Swords Bard is my current favourite. Put your points in Charisma, use the Dexterity gloves from the Creche and the Diadem of Arcane Synergy which adds the spellcasting modifier to weapon attacks and it makes for a very entertaining, mobile character build that felt it suited Astarion's personality extremely well.
