For postworking you will need drawing tools, layers, layermasks and layermodes. All of these are available in PS Elements. It is only with clipping groups that PS E does not handle - but you do not need those. And you need the big brother for CMYK: if you bring your work to a quality printer and printing multiple copies. But that is not needed for you, I guess

If you have the money, go buy Photoshop. But I doubt it that you really gain that much from using the big one, since all you need is in Elements. You also migh get frustrated because the menus and other things are in different places in Photoshop.

Take the time to get a Photoshop demo. You will have 30 days to decide whether or not it is worth the money. (Or use that money to buy a Wacom tablet....?)
Remember that students can get PS legally for a lower price. All rules can be found on the Adobe website.

Jacqueline