Do you redecorate ?

It depends who they marry. If it's the next heir in my legacy play or the next King or Queen in my royal save then I redecorate the bedroom if need to and a couple other rooms for them. Otherwise if they don't have the money to buy a new house or even a plot of land they will move in. Sell all personal belongings they don't want to keep. And once they have the money for empty plot of land or a house they will buy and decorate that one to fit them both and growing family as it grows

I don't redecorate based on individual sims as far as furniture type, color. Of course, If the sim is a bookwork, I will make sure to have a bookshelf and nice place to sit nearby, or musician etc. I do like to change the general appearance of my house/rooms every now and then. It keeps things fresh and a bit more immersive perhaps. Like I will change the flooring type and color or wallpaper etc. One thing I learned was not to focus so much on the color of the furniture or item at the time you buy it. Instead, once you have a room put together go to build mode and just press X on console (not sure about PC) and your shortcut to all the colors possible for that item, so you can make things match in various ways. It's much easier and better to do it this way then to worry about color when you're buying the item. But no, I do not redecorate based on a sims like or dislikes in general.

This has never crossed my mind. I always leave my houses as in. You've definitely given me something to think about next time I move someone in!