LOL, they sound very sweet.
As to the vaccination, unfortunately there are several strains of FIV. The vaccination works very well in the South (U.S.), but in the NE (U.S.) it's useless.
Our cats are indoor only, and the virus (usually) cannot be transmitted by casual grooming or sharing of food bowls or litter boxes. There have been cases of the virus being passed within a home, but those involved already immunocompromised kitties. Usually the problem is when cats are allowed to roam, not between indoor-only cats. Even so, they still do not understand the route of transmission, only that typically it requires a deep tissue wound by a cat infected with the virus.
What is known is that the virus survives outside of the body for a VERY short period of time - a few seconds to a few minutes. Cats that are not spayed or neutered and are allowed to roam are at the greatest risk, as it's usually a result of mating or fighting over territory, though just allowing a cat to roam in an area where there is FIV puts a cat at risk. Thankfully, so far, no other trapped kitties have turned up positive (though the test is completely useless for kittens 6 months and younger).
To date, research indicates it seems to be a virus very similar to HIV in people when it comes to transmission. Sex and sharing of IV needles is the most common form of transmission. Sharing a water glass has an almost zero probability of passing the virus from one person to another.
As our kitties are indoor only and don't fight, we felt the risk was worth his life - especially as the FIV rarely kills the cat, it's the immunodeficiency that puts them at risk of dying from something else.
We're VERY careful in our rescue work, and thankfully in all of our years, we haven't brought anything home that has caused any of our other cats to ever get sick with something like even an upper respiratory infection. *knock wood*
Because of our rescue stuff, we work with a lot of area vets. They all have some clients that both FIV+ and FIV- kitties in their homes. Though FIV first appeared in the late 1980s, our longest-practicing vet (27 years) has not yet seen a case of cat-cat transmission within an indoor-only home. Of course it doesn't mean it can't happen, just that the probability is very, very low.
FIV kitties are prone to gum diseases and problems with their teeth, so he'll be getting his dental every six months.