About the biggest argument for Elements of Photoshop is price... hundreds of dollars.
Here's a site that outlines some of the major differences. The tone is a bit Phothshop biased IMO, but if you look past that, the information is accurate.
http://simplephotoshop.com/photoshop..._photoshop.htm
Unless CMYK is a must have (not available in
PSE) and based on what you wrote about your background and near-term needs, I'd say go with
PSE and learn to use it. If/when you run up against
PSE limitations that full-blown Photoshop addresses, you can take the leap to
PS knowing 95% of what you learn in
PSE is transferable to Photoshop.
HPE provides some workarounds, e.g., playing actions, curves, layer masks, that answer the most common complaints about
PSE limitations. While not as easy to use as the native Photoshop functionality, they do work.
~Danny~