To save everyone's time, I'll just point out that I cannot accept maps that rely on custom artwork in the atlas. Details here.

Looks like your current map is in the basic CC3 dungeon style. That style doesn't have additional catalogs, as it is just a vary simple preview style for dungeons. All symbols are in the symbol catalog being loaded with the map, the one currently in your symbol catalog window.

There isn't a setting for a default save location, but it should be remembering the last folder used.

For a workaround, you can also use Windows' only features, such as pinning a folder to quick access or making a library, since these are easily accessible from the save as dialog.

Yea, this particular article was written with the intent to hide things that are "outside" the structure.

When it comes to your house, that's a very tricky thing if you let the players have access to the entire map, as that clearly allows them a different view than a person there would have, and instantly reveals things like too-thick walls or suspicious corner. I would be tempted to give the players a modified version of the floor-plan, where the rooms are slightly larger, maybe the house slightly narrower to hide such thick walls. Only if they actually start measuring things should they be given the true map so they can see that there is something wrong here....

Of course, some players may call foul on such an approach, feeling mislead. And it also means preparing two maps instead of simply hiding something.

For reasons like this, I usually never let the players see the entire dungeon. I practice hiding everything they can't currently see. (Using MapTool hooked up to a projector)

Bit nitpicky here, but it looks like the players version have been hidden by simply overlaying a polygon on top of things, I can still see some floor edges there.

I would suggest using separate layers that can be toggled to completely remove the entites, and possibly draw in a full wall on the player layer as well instead of the thinner one. I have a blog article on this.