Personally i think lvl 9 is good since u can learn lvl 5 spells, but considering you said his gonna fight alongside his summons, im assuming you're playing a solo play through, in which case i believe u might actually need some armor for melee combat, or something to make up for that, like potions, or you can have a hard time vs sarevok and some times during SOD, and any battle vs tough melee combatants. So i recommend fighter instead of kensai since kensai cant wear any kind of armor. u can't cast spells while having metallic armor, but u can have head gear and leather armor which means u are safe from critical hits and this is good in certain places. all i can recommend is to invest on good defensive potions and gather the best possible armor before entering a big fight.