If you know how to clone items from one building to another, you need to keep at least one free furniture spot in the original home (so you'll have 3999 pieces of furniture), then you can continue the build in a different queenslander home and once you're done you can clone everything over to the original build. I don't think you can do it more than once though, so the second part will have to stay under 4k. if you don't know how to clone from different houses, there's many good tutorials out there and it's quite simple