You may want to look into external project management/story tools as well. It might be easier to flesh out ideas and progression not directly within the UE and rather create everything you need outside of it. It’s a more linear and independent approach that doesn’t conflict with the actual game files/assets.
LOD -> level of distance = you have different stages of meshes with different tri counts (e.g the first stage has around 1000 tris, the 2nd one 500 and the 3rd one 100)
light baking -> when you use static lights you will have to do that. So the shadows are getting baked on the lightmap instead of being rendered in realtime
Just to add to that. LODs are very important to open world games in particular, so that when you get up close to something like a landscape in the Kite demo etc it has lots of detail, but when you move away from it, it loses detail so its cheaper to render which means your frame rate stays high.
There are lots of different types of lighting but you can group them into two categories, dynamic and static. In dynamic the sun moves, the shadows move, illumination on objects changes. Whereas with static or baked lighting the reflections and shadows etc remain static for every object and do not change. Obviously dynamic looks better in-game and makes levels more interesting to look at, but static runs faster and will run on more devices…