The end goal with Griff was to cast the most powerful spell(s) possible. This required the highest magic skills possible, so becoming a vampire was the obvious route to go. It also led to the secondary goal of being the frailest character possible too: 100% Weakness to Fire and 100% Weakness to Magicka, thanks to the combination of Altmer race, Apprentice birthsign, and vampire (de)buffs.
That was the extent of Griff’s motive. He never joined a faction or completed any work for Caius. I may have had the intention of joining the Mages Guild and the Telvanni, but I stopped playing after finishing the Aundae quests. I vaguely remember getting burnt on grinding my stats to 100 before transforming (that’s the only way to go above 100). Powergaming isn’t very fun. So Basically, the run ended when I had 140 Willpower, 150 Destruction, and a selection of spells that did thousands of damage in seconds. Not bad.
All in all, it was a memorable playthrough. This was the first (and really only) time I played as a vampire and did the quests (for one clan, anyway). I still never did the quest to cure vampirism to this day. I also missed-out on running through the Mages Guild and Telvanni as a vampire, but I’ve done those two factions countless times. I really loved mages in this game as a kid.