Came out beautifully.

Use Draw -> Hex or Square Overlay

Note that CC3+ doesn't allow automatic creation of grids with variable thickness. You could either make two grids, or, since it sounds like you won't have that many whole-inch squares, you could probably just change those lines manually. The grid is a grouped entity, but you can unlock groups by hitting the Locked button in the bottom right, and now you can just use :CC2MCHANGE: on the grid lines you need to make thicker.

Note that you normally make maps in CC3+ in real-world scale, not paper scale, so grids aren't normally specified in inches, but since this is a rather abstract map, then perhaps you should just treat one map unit as one inch in this case.

All images in posts are scaled to 1500px, regardless of the size limits. I thought I wrote that somewhere, but who knows where.

Images in posts are generally intended to be viewed in the post so allowing images much larger than fits in a post is generally a waste of bandwidth, and slows down page loading.

There's nothing wrong with putting WIP images in the gallery though. You may wish to have a separate album for them.

It's more about the tone of the settings than the colors of the map. Just think "the world is not a happy place" and adjust whatever you need to accomplish that. Ruins, war and conflict are all central elements.

Not really. The main important points for me is that it is correctly scaled and only include the "approved" artwork, the rest is handled my my macros.