I had S rank since the beginning without even trying. I got lazy and have two rooms with full cute sets in different colours. They must really like full sets.
The last score I had was around 150,000 (S rank). I got all of the plaques and trophies, so I thankfully don't have to worry too much about maintaining it!
If anyone's curious, I only decorated the main floor's rooms. The upstairs and downstairs rooms are completely filled with DIY recipes, placed furniture, and placed fish/bugs waiting for CJ/Flick. I think that's how I really was able to get so many points, not because of my home decor skills...
I'm at like 125,000 something. Do y'all know if they count the basement? I've added a lot of ironwood furniture to it now so I hope that'll bring me up to the gold trophy