Let's see... when I ran this for my family I was mostly winging it on NPCs; the basic thought process was write down the NPC's four attributes and one or two skills, each on a scale of 1-3 dots, and you're good to go.
If they might need to fight your PCs, the minimum they need is: at least one skill that they can use to hit you with; a Strength score and a Toughness score (I really would just give them a rating in all four attributes though); and a set of health levels to mark off (if they're normal, fragile mortals or intended as disposable mooks you might decide not to give them a full suite of six). Remember skills are freeform, so "corrupt cop" (obviously the corrupt cop has a gun and can do a car chase!) or "investigative journalist" (obviously the investigative journalist is super perceptive and will see through your lies!) or "vampire hunter" would absolutely count if you're comfortable with your own ability to fairly interpret something that broad on the fly. This of course also allows you more flexibility in allowing them to not fight your PCs if the story calls for it.
All that said, character sheets are simple enough in the way I stripped them down that for an important NPC you can probably get away with straight-up building them as if they were a PC (something I would never bother doing in vanilla V20).
If you have an elder vampire, I would increase their maximum number of attribute, skill, and power dots accordingly, and give them a few extra dots to assign beyond the 8/8/3 spread that PCs get. You might need to play with the numbers a bit to find the right balance but shooting from the hip I want to say 5-dot max for someone you want the PCs to be able to go up against directly if they're clever and lucky, and 7-dot max for someone who will squish them like bugs. I would also not hesitate to build a custom power or power implementation for an ancient vampire I truly felt needed it.