for summons keep int as low as gear requirements demand. At lvl 21 it's still 14 - don't know if it goes higher later.
level con and wits. constitution for the obvious vitality boost :P.
wits so you start first but also so you can utilize savage sortile talent to scale into late game I don't think mage works without it. you should also focus on wit and crit% on equipment. the more sockets your amulet the better - fire runes :P while 14 int seems low you can put power frames on your fire runes to boost it up to 30 even. on the nameless island you will meet a master who can also trade in 5 of your finesse i think for 5 int (don't quote me on that one - it could be another stat).
you should stick however with what you want :P. summoner is a great party support. damage support through summon, firebrand damage aura if you pick it up in fire tree. soul mate and rally make for great healing support, 4 in necro allows you to revive your party members with last rites - if you combine that with shackles of pain and you deal a critical strike you can deal insane damage when ressurrecting a fallen ally(I advice using living on the edge beforehand =D).
necro / warfare is physical focused. so you would probably pick up a normal melee weapon. necro damage is bad. very bad. approx 50% of what other mage schools offer in raw damage. reason for that is probably enemies not having physical resist, so necro is never situational and very reliable.
still you would want more points into strength but some int won't hurt. widdle down enemy armor with melee skills then debuff with decaying touch etc.
necro warrior you can think of as a berserker. High lifesteal allows for more damage and less con. Later on you become tryndamere with living on the edge and death wish.
