I found a guy selling a rug and chair in the karaoke bar in Central. I honestly couldn't tell what had changed when I went back to my apartment.

All of the other safehouses you get in the game are fully furnished and fine looking. I thought all of the upgrades were just for the shitty hotel at the beginning?

You can also by a pet (bird in a cage) from someone in the first area. I don't think it's marked on the map. Hope you don't have to feed it, cause I've never looked after it after buying it...

I ended up buying something every time I found a guy selling something, I never ended up noticing any of it.

you can buy a painting from some british dude near your boat safehouse i think.