-Make the high poly models like you planned on.
-Make the low poly versions of them for use in the game scene. (The level of detail the low poly will vary based on your preferences)
-Bake normals from the high poly versions using xNormal or some other program you like.
-Use the low poly model in game with the normals baked from the high poly model to bring back the detail you lost when you made the high poly model.
-If you want to go even further, you can set up an LOD system so that you are only using the more detailed models when they are in view/proximity. Look up Simplygon for a good example of what LOD is.