I vaccinate mine at home, because with this many cats, I would be in the poorhouse if they all had to get their shots from the vet! It's not that hard to do, in my opinion the hardest part is the looks you get for an hour or so afterwards from the kitties. (Mom, how could you?!?)
I buy the 4-in-1 vaccines from www.drsfostersmith.com
and they do come with instructions. However, I am a registered nurse and not a stranger to giving injections, so you might want another opinion before making a choice.
I believe in PA the only vaccine you can't give to your cats is rabies, that must
be vet-administered for legal reasons. The Drs Foster and Smith website sells cat 3-in-1, 4-in-1 and 5-in-1, as well as Feline Leuk and FIP vaccines.