Effects cannot be trimmed. You'll need to cover it up with something.

Personally, to prevent things from extending through a wall and into the "nothingness" behind, I like to use a mask that is made up from the background with holes punched in it for the dungeon (using a multipoly for that) and put that on top so it basically covers up everything outside the walls, including unnatural shadows.

Notice that this behavior can indeed be automatic with the drawing tool, and it is that behaviour the instructions was written against, but it seems that most drawing tools doesn't use it. But if you edit a drawing tool, you'll see it has a setting labeled attach mode, which can be current settings, on or off. Current setting refers to the global attach option, the button down in the lower right of the main gui. On or off is just forcing it to be always on or off. Right click the attach button in the lower right to select exactly which attach option to use, I think endpoint is the default. (The drawing tool can unfortunately not specify which attach option to use, only if it should be used or not)

There won't be an automatic snap grid point in the centre of symbols. The snap grid has it's origin in the origin point, the very point you are attempting to move, and you wanted to move it because it was at the edge and not the center of the symbol to begin width. If the origin is at the edge, there will only be a snap point in the center if it so happens that the distance to the center of the symbol aligns perfectly with the grid size which is just a luck thing. Snap grids are after all calculated as a fixed grid starting in the origin, not magically associated with the image. As Sue says, you'll have to judge by eye.

No file. The default colors are hard-coded into the software.

Yes, with presets, you must apply them manually to each map. But the advantage it that it can be done with existing maps, and not just with apply to new maps.