For a caster favored soul, high Charisma (obviously), 14 Dexterity (you get medium armor so a +2 Dex is the highest Dex bonus you can get from medium armor) and Constitution (for concentration, hit points and general survivability). Life domain is attractive because it nets several strong low-level spells a sorcerer would normally not have access to: bless, cure wounds, spiritual weapon and lesser restoration. Bless+Sorcerer attack cantrips+Spiritual Weapon (which is a bonus action) gives an increased chance to hit and strong round-to-round damage. And never underestimate the ability to cure your own wounds, especially with twinned spell.
If you only want to focus on arcane spells and don't care about encroaching on the cleric spell list, both the Light and Trickery domains offer strong options. Light offers many strong blast spells you would have wanted anyway (burning hands, scorching ray, fireball, perhaps wall of fire) as well as faerie fire, a strong first level spell you would not normally have access to. This frees you up to grab some utility choices with your precious few spells known. Trickery is the reverse, offering strong utility and defensive options (mirror image, pass without trace, blink, dimension door, polymorph) leaving you room for attack spells.
I don't play gishes, but I hear that war and death are the domains of choice for that. Although I think life domain could work for that as well because of bless. A recommended build for an archer gish I've seen is Fighter 1 (archery fighting style) /Favored Soul 19 (life domain). Archery fighting style + sharpshooter feat + bless is deadly.
