You have pretty open leeway but the clan aspects should be noticably vampiric as far as lore is concerned. Some kind of blood or essence drinking is essential to any Vampire clan as is the general undead designation, but daylight vulnerability isn't a requirement (one could find their flesh shimmers in sunlight but otherwise suffers no adverse effect, for example). Same with other common tropes such as garlic repulsion or obsessive counting.

The final major requirement is that they do have some specific way to properly kill them, whether by beheading, staking the heart, or other means.