If your room looks crowded its going to look like your rich...and it will also look like your bragging. No one likes a "crowded room" so here is how to tell if YOUR room is crowded!
If you can NOT move around in your room...move some things...then if you still have that problem, move some things OUT.
If you want to have a "WOW" house to WOW!! your friends....make it short and sweet. Add some exclusives, or things like that to make it sweet and follow advice above to keep it short (non crowded)
It is OK to have a storage room for your trading items...but if you put all your items in a room to decorate...some might like it but most will turn away.
If you find yourself with a large room and only put (example) 10 items...it may look TOO empty. So make sure to have others "overlook" your room to make sure its not too empty, nor too full.