This is one of those questions that's especially tough to answer without any context. Even if you're planning to DIY the execution of the project, you would be well served paying for a 1 to 2 hour consultation by an interior designer. They will provide invaluable advice about what is appropriate given the size/style of your home, the budget and local/regional style preferences.

Best wishes for a successful project.

Crown molding can be a very nice touch, but it does depend on the style of architecture (it may look out of place in a very modern home). Pictures of the rooms would help. You might want to look in Houzz for similar homes that have crown to get an idea (search under crown molding). Also, there are different styles, so some are traditional but there are more modern versions of crown molding that can work in later model homes.

Update? In my opinion, crown molding is outdated.

I dislike crown moulding. I pulled every bit of mine down, and bundled it all together and put it out in the rafters of the back shed. Someone else can put them back, if they choose too. This is the second house, I have pulled crown moulding off and stored it all away .