Yeah, I think I agree that a lot of those starting questions are subjective, depending on what the map is being done for.
If you’re just making a general map that you want to upload and let people toss in to their projects, it’s probably better to air on the side of less is more, that way the game designer can use what you’ve constructed in whatever vision that they might have for using it - try to not “force” a specific starting and end point, try to make multiple avenues through the map to allow for any possible objective or player movement, etc.
If you’re designing something specific, then it becomes a more focused question of what you want the flow of the map to be like. Do you want a slog of a forest for setting or slowing down the player? Or do you want sparse terrain to act as cover from the enemies that are in the way? (So, yes, I do think enemies can substitute for terrain, and I would honestly encourage it if you want the player to need to be a little more risky instead of just hopping from terrain to terrain for the bonuses.)
When I’m making a map, there’s one of two paths that I usually stride down - if I’m referencing or “replicating” something, then I try to recreate that design in the style of what’s available to me, while still accounting for the above. If I’m making something brand new that’s for a project or just off of an idea that I had that could be used in a project, I tend to loosely sketch out the overall design of the map first on a notecard, using rough dimension lengths to figure out the overall size of the map before starting. This helps keep the different elements of the map in my mind as I’m working and helps me visualize the intended flow as well as helping make sure that I keep things “general” enough to veer from that flow if that’s what someone might want to do.
For Fog of War… I’d say that good map design can help, but you also have to tailor it knowing how the AI is going to approach/abuse it, I think. Good map design in general will help a lot of things, though to answer the final prompt question there, I always try to strive for making things look as complete as they can (including correct heights, correct wall shadings, etc.), though I will allow that to slip slightly if the tileset in question has no exact way to do what I want with a map on the gameplay angle without looking weird. But, I do try to make sure things look good and correct in addition to having a well-designed map.