I'm not sure I understand why you would need to vaccinate all your cats if the one cat is confined outside. The crate I linked to can be used inside your house. I can understand heartworm being transmitted through mosquitoes but heartworm prevention doesn't need vaccinations if you use Advantage or some other monthly topical treatment.

Thankfully, Curie has not had a pee incident since I started confining her when she's not under supervision.

I am also transitioning Curie to being an indoor/outdoor cat because she has always been extremely interested in going outside and I figure she will much much prefer to pee outside than inside. I did make sure my cats' vaccinations were up-to-date before I started letting her outside though.