The easiest way to use textures (fill styles) from another style is to first make a blank dummy map in the style containing those textures, then in your actual map, go to Draw -> Insert file and pick your dummy map and hit ok. Once you return to your map with the dummy map on your cursor ready to place, just hit escape immediately to stop placing it.

For most maps, just set the 'Restrict image to map border' option in the export options dialog, and it will take care of it. If the map is somehow missing a map border, use the rectangular section jpg file type when saving, as this will cause CC3+ to prompt you for the corners of the export before saving the image.

Yes, just hold down the control key and click on an entity to deselect it.

To add to Quenten's reply, you would do that by using the regular :CC2MCHANGE: command.

No, that's actually a very different issue (but somewhat also related to time). You may remember the old version of vanilla used whispers embedded in the discussions themselves, a feature not available in this version. But those whispers caused the read counts for those threads to be off when they were removed from the discussion and turned into PM's during the upgrade process to this version of vanilla. It affects all discussions that contained whispers, but it works itself out for active discussions as people continue posting in them.