This build is based on Fudgemuppets Frost Demon build except a nord who wilds a sword and lightning rather than a Orc wielding a war ax and frost I also based this build of of the Vampiric Electromancer build by Plauge713.
This Nord was born in the first era and had been a soldier and a student of magic one day while walking through the woods one night he was attacked by vampires they made him one of them and he found he had an affinity for shock magic and for centuries the the group of vampires traveled around Tameriel the Lightning Demon studied shock magic more and more becoming very powerful.
One day the demon and his companions came across a group of people the leader of the vampires summoned a storm but what the vampires hadn't known was there was a powerful mage with them he managed to deflect the storm away and the group of humans proceeded to slaughtering the vampires though the vampires fought back and killed the humans except the mage who had killed all except the demon but the demon had still been practicing his sword he cut the mage in half though he was the last of his group of vampires not wanting to spend time alone in a cave he returned to his home in Skyrim where he will hear about the Volkihar clan and he will track them down.
Using the alternate start mod you will choose to be a vampire in a secluded lair you will then start looking for the volkihar vampires I would just if you know where it is go and you think you can get through Dimhollow find the Dawnguard and go and proceed with the quest.
For factions I would join the Dark brotherhood, the dragonborn story line, main story line, the Volkihar Vampires, you could also do the college of Winterhold for spells, as a nord you may think about joining the Stormcloaks but thats your choice have fun with this build.