ur not nuts completely
i totally understand being protective and buying a house that fits the needs of your dog. i bet it's just malnourished or maybe really old. i wouldn't lead my head right into parvo from the things you described.
we bought our house because the backyard didn't make the pups have to climb stairs from a deck down or anything and went right out to the yard which was fenced and nice. i understand wanting a place for you puppy to be safe and healthy. i wouldn't worry about parvo tho. he's had his shots and he should be just fine.