i want to play a character style that I haven't done before and i'm having some trouble hashing out what skills will be useful in the long run. I've never played morrowind with any magical capabilities or used a spear... always leaned towards stealth or brute strength.

I've settled on a few details but would welcome some suggestions to complete the build

Female Dunmer with Spear, Illusion and Medium armor as major skills. Alteration and Restoration as minor.

haven't settled on a birthsign yet but was leaning towards the mage

this character will not partake in the main quest but will join the mages guild and the imperial cult. she will likely join house telvanni but i haven't decided on a great house yet.

any thoughts or insight is appreciated

I have a similar character but a Nord. I picked Strength and Intelligence and Lady sign. This may seem a little wrong for a magic using character but really having only 100 magicka is enough for utility magic and having the extra health and strength is worth it. Plus extra Personality if you want to train Illusion.
For skills:

Restoration - hard to raise and very useful at the start
Alchemy - starts high enough to make potions right away and can be used to advance in Mages and Temple.
Illusion - builds Personality and advancement in Telvanni, Mages and Morag Tong if you want that.
Medium Armor - good early armor and if you do the Temple, a great piece as a reward (Nord gets a big bonus too)
Spear - Decent damage and excellent reach to stay out of trouble.

Enchant - all purpose and favored skill of Cult, Mages and Telvanni
Marksman - good back-up skill
Conjuration - bound spear and bow. Could swap with Medium Armor to use right away.
Alteration - open, water breathing and levitate
Mysticism - favored skill for Cult, Temple, Mages and Telvanni plus good utility spells.