Generally, for a whole-world map, Equirectangular works fine. But it distorts shape and area as you get closer to the poles, so it isn't as good a projection for areas far to the north or south. Here something more true to shape may be desired, like the Equal earth projection. For the polar regions themselves, something like the Lambert Azimuthal Equal-Area may be a good idea.

Basically, each projection in FT3+ comes with a descriptive text, I advice you to read it.

The Digital overland comes from the Vintyri Cartographic Collection.

It's just a case of DD3 vs. SS4 menus. When SS4 was first released, the DD3 tools wasn't part of the core package, so SS4 shipped with a menu set that brought up the standard drawing tools instead of the specialized dungeon tools. Just hit the :DD2: button on your toolbar, and the room button should bring up the desired dialog.

Using @ is completely fine, especially when it is in context, i.e. to refer to someone saying something earlier in the thread. It is also fine when referring to something a user did earlier/elsewhere, for example "I am following the instruction in this blog by @WVFaeryWoman but I don't understand the steps.....". It is bad if you try to drag unrelated people into the thread by spamming your post with @-mentions, for example posting a request for help, and then filling it with @-mentions of the names of people you know gives good help generally.

If people don't like to be notified for @-mentions, they can control it from their notification preferences.

This can happen if you already have the other volcano in your map (because you have placed it at some point). Open up symbol manager (Symbols Menu -> Symbol Manger) and then either hit Purge (will remove all symbol definitions you have used in the past, but which are not part of the current map, or scroll down in the list until you find the undesired symbol, click on it to select it, and hit the Delete button.