This is a neat mod, and so far it works quite well. for the most part.

Testing out the mod, i aged my guy from 18 up to 300 years and he turned into an old fart. shouldn't Vampires remain young forever if they were turned young?.
You should make the vampire traits work like the vanilla immortal trait, there age should essentially freeze once they're turned. if they were a young man when they were turned they will remain young forever. if they were turned at around 30 or 40 years of age they should remain at that state, and if you turn an old man (ew) he should eventually revert to his middle aged state at the very least.

And hm, not 100% on this since i never tested this fully but..

Since vampires are dead, they can't/shouldn't have children in the normal fashion. so there fertility score should be that of a/ or worse then a eunuch. so if i successfully turn someone by feeding on them that character should then become my "child". and the turned character will gain a "Loyal to Master" opinion modifier. (plus 500 opinion for their master) once they fully turn.

They should still have there human parents visible on there relations screen but your characters picture is added there next to them.

I could provide more ideas if you want..but i'll just leave it here for now maybe. Thoughts?