The LMT part you point to is detailed enough to justify a 4th axis if you're going to make a few. Or you can just make fixtures to hold the piece for each operation.
There are benchtop machines that are rigid enough to cut stainless steels with high precision, but obviously they don't have 18" travels. Larger machines that will cut 18" and fit in the basement probably won't hold the kinds of tolerance you would be happy with. And a machine that will make 18" parts to precise tolerance won't fit down the stairs.
Time for a new house with a bigger garage.
