Both of these viruses can be spread through bite wounds, and both are incurable. It is also a good idea to have your veterinarian check stool samples for any parasites and be sure neither cat has fleas or ear mites which can be easily passed to one another. Once both cats are determined to be healthy, you can begin introducing them to each other. It is usually best to let the cat who has been in the household approach the newcomer. Put the new cat in a safe environment, such as a crate, so the established cat can approach, and they can both see each other.
Some cats take to each other right away while others take a few days or even a few weeks.
There may be a few dominance scuffles along the way, but they usually subside. I've been noticing blood on them after he's done playing with them. He's acting fine. Puppies loose their baby teeth when they are 4-5 months of age starting with their incisors or front teeth, then their molars, and finally their canine teeth. The blood you are seeing could certainly be due to the loss of a tooth or from his adult teeth breaking through his gums.