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.

Turn off snap (lower right corner) when working, this allows you to place nodes right outside the map border, and let the functionality that restricts it to the map border kick in.

With snap on, you are basically just placing nodes at the edge, but not over it, so it treats it as a regular corner. Note that you can achieve this with snap on too, but you need to move your cursor much farther out from the edge of the map to hit the snap points on the outside and not those at the border itself.

Bring up one of the Schely trees for editing from the Symbol Manager, and then use Tools -> Distance to measure the height of it.

Now, edit your own symbol, and just scale it up so the height matches.

Note that your symbols should be edited in the source symbol catalog where you have them, if you edit the symbol from within a map where you have used it, only the copy stored locally in the map will be changed. Also, when you change it in the actual symbol catalog, be aware that maps that already use the original smaller version will continue to use it (because symbol definitions are copied from the catalog into the map on first use) unless you first purge it from the map.