After you finish paying of your house you have theme challenges which means you get points for having furniture from a certain theme, matching house exteriors also give ya points
For now I know I got over 100k point on an alt character with a complete fishing set, balloon set, egg set and a few lucky items
Another tip besides having sets is fung shuei-ing the crap outta everything lol
Congratulations on hitting this goal. You will be shooting for the gold exterior parts in no time. Even though they are strict with what can and can't be in the house during this time, it fun to accomplish it. Then you can change your house to whatever you want. At least thats what I did. I pulled out everything and made my house what I had always dreamed it should have been, a resort. Not a bed in every room. lol.
Congratulations! I had only 3,000 points (I've only had my town for nine days), but I got the princess theme from someone so it's going to increase like crazy. ^~^' You'll be hitting your next milestone in no time, I'm sure!