Level design is fun, especially when you are creating the puzzles and progression around your own mechanics.
There are various heuristics to follow when creating levels, such as not creating the levels in order that they are going to be played in game. You take the best levels and place them at the begin and end of the game, and usually the best levels are created at the end or at a time where you are very comfortable with creating the levels for that particular game.
Be aware of how all the integrated systems work, so that you don´t design your way into problems that are a lot of work to solve. Not place too large objects that obstruct the camera view of the area or the visibility of your characters. As for animation authoring of movable objects, be aware that the Animation authoring system in Unity is only set up for animating items in world space. If you need to copy a prefab with animation that influences objects or areas, you are better of authoring the animation in a DCC app and bind to the skeletons that you export from there.
Me and my brother got a few puzzle items working over the last couple of days and have an almost finished puzzle area. There was a lot of tinkering with set up in Unity and how to use its features properly to create the levels optimally. Navigation meshes, off mesh links and moving items between navigation meshes was taking up most of the work. Problems we need to solve properly to create the puzzles and levels. All of this is just created using boxes and simple primitives.
There will be a lot more box areas to create over the next few weeks, and at the end of that, we will need some testers to break everything.
More to come in a few days.