Robert Neville's relationship with alcohol?
It is clear that Neville had an alcohol problem long before the plague and the death of his family. At the start of the book, his drinking was partly out of boredom, partly to forget what he had seen during that day. However, by the end he says that he didn't need to drink any longer, so he wasn't an alcoholic.
the vampire virus theories presented in the book?
The book tried to give scientific, or at least, realistic reasons for the Vampire myths and lore than we all know, and that was written by Bram Stoker. I respect the idea, but I don't think it really works. The "Cross" is one example where he says that a Jewish Vampire has the same reaction to the Torah, but sorry, that isn't the way Vampire lore is written elsewhere. Vampires are mythological or Satanic creatures that cannot be explained by science.
The Walking Dead franchise has very similar problems when explaining the "undead" with a virus and it doesn't work. If the body has begun to decompose, then it will not function. No amount of fresh blood is going to cure a decomposed body even if it 'satisfies' a virus.
Ruth's people were living with the virus by taking a pill made of blood and some drugs, and not turning into full vampires. I think I can just about accept this if I accept that vampirism is caused by a bacillus.
The Walking Dead also tried to do this by doing a big reveal that everyone had the virus within them at one point, but back-tracked on that later because it was much more exciting if people who got bitten turned while still alive.
None of his protagonists are heroic.
His protagonists are unwilling and reluctant, and they have faults, make mistakes, and are human. I think we need to really ask here what is heroic and who are heroes. People who have no scruples about killing others are lauded in wars as heroes, and we rarely question that. However, frightened individuals who find the courage to save others without much thought to their own lives, are much closer to what we expect from our "heroes", and they make better role models for heroic action. Most heroic medals, on the other hand, are awarded to war heroes, but there are some civilian medals awarded to people who never killed anyone - firemen, lifeboatmen, police officers and also ordinary people - ordinary people who were probably unwilling and reluctant but still jumped into a river to save someone from drowning in any case.
There may have been a sexual element to him targeting female vampires
He said that when picking up bodies in the morning that it was always female vampires. I think the females just came closer to he house and were easier targets for him. His sexual attraction to them wore off as the book progressed.
male vampires were often depicted as targeting female victims so this is a parallel in reverse since Nevile is in the end, a Dracula counterpart.
This is what I took from it too, that there is a male dominance in this vampire lore.