You asked these questions rather late on a Friday evening (here in Sweden, at least). If you wait until Monday there might be better answers from a 2D-artist than from me as I am not an artist myself. Anyways:
* As you are asking in the PDS' part of the forum, you get to know that we have four 2D-artists (at least, that's how many there were last time I checked...) that all paint loading screens and other stuff. Covers might be outsourced to a third party, but some has been made in-house, such as the cover for March of the Eagles which was painted by Adrenaline. It all depends on how much work the 2D-artists have to do. That is especially true for promos, which might be painted in-house or outsourced. Sometimes it is cheaper to use a freelancer for stuff like that.
* I think that all our 2D-artists use Photoshop and have some kind of pen tablet like a Wacom or similar. How they produce things depends on the project and what we need. The rest of the question I think I'll let a real 2D-artist answer
* Nice idea, have you suggested that here? http://forum.paradoxplaza.com/forum/showthread.php?801303-Paradox-Extra-wants-YOU!