FIV wouldnt be too much of a risk, it can only be passed on through a deep bite. I personally do full bloods with thyroid even though my vet says I dont need to do the thyroid, normal bloods will indicate if there is a thyroid issue, as it affects the liver readings, but my reasoning is that if they show it, and we need to test, they need more blood, so they might as well do everything in one go. The other thing I would ask to be tested, either that day or aftre you get him is blood pressure, as that is one of the reasons for blindness. Good luck, and good on you for considering an oldie with a disability. Have you done any reading on blind cats? There is a really good new book out, I dont know where you get it from though, as my vet lent me her copy.