Koi and Goldfish Mix???

Well I have been scoping out the good Pond Fish stores in my area and found a couple with very nice, healthy fish. My original plan was to go with 4 Comets and 4 Shubunkins...............and that's it, but I fell in love with some beautiful Yellow Koi at the one place and I'm thinking of just putting ONE of these Koi in with the other Goldfish.

My pond is only going to be 800 gallons (3 feet deep), so I didn't think that it was really large enough for Koi, but could I get by with just ONE?

Also, would the one Koi feel at home with 7 Goldfish, or would he/she feel out of place? Thanks, Jimbo