Some things to consider:
Is vampirism a disease or curse?
This one you have answered.
Is it ONLY humanoid blood? Or, any mammalian blood? Or, could even "cold-blooded" blood work?
About the "sunlight" thing:
Is it only "direct" sunlight (can be outside but must be in shade) or, "any" sunlight?
Or is it a "nocturnal" thing (can ONLY be active during the night)?
Is it "sunlight"? Or a specific part of the spectrum (i.e. - ONLY ultraviolight light)?
Is it actually "blood"? Or, is it the actual life force (such as the movie
Lifeforce)? Or, is it a combination?
Can a vampire be "good"? Or, is it only an "evil" thing?
Does a vampire live? Or, is it an undead thing?
How often must the "blood" thing be satisfied? Once/day? Once/week? Et cetera.
Must the vampire drink "all" the blood? Or, would a smaller amount, such as a liter, suffice?
Is the "making another vampire" a thing of "will" on the part of the vampire? Or, is it spread like a disease and only being bitten makes you a vampire? Does it require a complete draining of all blood? Or is it a partial thing?
I did GM a player who fell in love with a vampire and chose to become one herself to be with the one she loved.
My rulings were:
- They were NOT nocturnal. They can be active any time of the day.
- It was ONLY "direct" sunlight that caused the harm. As long as the vampire stays in complete shade s/he was fine. They also had to be fully clothed, preferably with hides or other impermeable "cloth", since actual cloth is somewhat translucent to sunlight (unless it is very thick).
- I also ruled it was only the "ultraviolet" part of the spectrum. Now if only someone could invent a good sunscreen...
- Of course, the "penalty" did apply during daylight, but became a bonus during the night.
- Any "warm-blooded" blood would suffice. No "cold-blooded" blood.
- It was only a "need" for blood, not the "lifeforce".
- I even ruled that a vampire could also gain sustenance from normal food, but still required a liter of blood at least once per 3 days.
- A vampire could be "good", but the "thirst for blood" was still viewed as being an "evil" thing.
- Once the town folk understood and realized the two vampires (he and she) were "good" and used their special abilities to aid and protect the town folk as best they could, the town folk actually came to admire and understand the vampires. Some even became very dear friends.
- A vampire did not need to completely drain all the blood. A liter sufficed allowing the "victim" to recuperate, taking about 10-15 days.
- Spreading vampirism is a "will" thing, meaning the vampire must "will" its victim to become a vampire, and need not drain all blood.
Well, I cannot remember more about this since it was about 30+/- years ago.
About the cloth thing. I know cloth is translucent because I had once spent about 12-13 hours out in sunlight turning the soil in a farm plot and still got badly sunburnt on my shoulders and upper back. After that time, I put on sunscreen everywhere, even if I was wearing clothes, and was going to spend quite a long time out in the sun.
rmfr