This is MY opinion, my knowledge. because I believe it is true doesn not make it true and others might have different opinions. Hopefully, if they do there can be a lively debate.
1. Vampires are non human souls trapped/reborn/contained within a human body. THe human body does not provide sufficient and correct sustenance for the vampire soul and so it has to take in additional energy. There are three ways it can take in energy... from living blood, from elemental forces such as storms etc and from the auras/energy of other human beings. Weres are simiar only the body is shared between a human soul and that of an animal
2. There are three kinds of vampires. Sanguinarians (sangs) only take blood. Psychic (psi's) ongly take energy from elementals/humans. Hybrids do both.
3. Vampires are born and not made. Vampires generally do not know they are vampires until they 'awaken' This often happens during puberty but can be much later. During awakening you gradually become aware of your nature. Most vampirs have already noticed that there is something different about them and many have gone through trauma because of it. Often the feelings of disassociation, depression, dispondancy, restlessness, tiredness, anxiety etc get worse during awakening but settle when the vampire become more aware of what and why they are. Awakening takes different forms from person to person.
4. I believe that the reason some people believe they have been 'changed' by the bite of a vampire is that when bitten the saliva of the vampire goes into the wound as well as the vampire energy and this triggers awakening in latent vampires.
5. The only physical difference we have identified are slightly elongated canines, changing eye colour, stronger and faster growing hair and nails, increased rate of healing. Tendency to 'see someone different' on looking in a mirror. WE DO NOT SPARKLE except in our sparkling wit and personality.
6. Because they are born into human bodies vampires age, grow and get sick just like anyone else.
7. Whether vampires like garlic or not depends on the individual, just like everyone else. I LOVE it. The garlic myth derives from the fact that garlic is a purifier and it was beleived that vampires are unclean and undead and therefore fear purification... same thing with holy water.
8. Most vampires burn easily and many have a sensitivity to sunlight... so we do burn :p Personally I burn at the first exposure to sunlight and wear sleeves whenever I can in the summer. I never tan... I burn I peel I go back to being pale. I have a terrible sensitivity. When I go out in even moderately bright weather, even in the winter, I have to wear sunglasses, I get ill when I'm in the sun.. headaches, faintness, weakness etc.
I think that covers most of your basis. Anything else you need to know ask. Although I stress again... THIS IS MY OPINION