Dynamic lighting, which is what is being used in your scene now with a Stationary light, is very efficient when not casting a lot of shadows, As your scene grows and the more meshes that are casting shadows you will likely see a performance hit. Tweaking the stationary light shadow distance will help. If you have meshes in your scene that are not needing to cast shadows or not benefiting from casting shadows you can turn that off in their details panel to help performance as well. (As a side note, for something to not cast shadows does not mean they can’t receive shadows)
For the previous questions though, for your brush something around 64, 96, 128 would work better for crisper shadows. For the landscape depending on it’s size you may want to lower that to 2 or 1 to generated a better lightmap resolution.
If you have any other questions feel free to ask! 