Complex Script For Automating Conversion of High Res Images to Web

I use Actions in Photoshop (currently using CS4) all the time, but have never delved into the scripting capabilities, so please forgive me if these questions are obvious.

The basic description of my project is simply creating web images in jpg format, from our library of high-res print images.

We're going to have one folder with a copy of all the images we need to convert. File types range from EPS, TIF, PSD and JPG.

The challenges (to me) are:

1. these images vary in orientation of being tall or wide; I need the greater of the dimensions, whether it be height or width, to be 400 pixels; and then I need canvas added to the other dimension to make the image a perfect 400 x 400 square. I don't know how to, or if I can, make PS choose the greater of the dimensions, to set it to 400 px.

2. some of these images have clipping paths; i need to use those paths to erase the background in the photos; the names of these clipping paths are not the same in every image.


So, the basic flow of the script would be open the file; set the max dimension to 400 px; add white canvas to fill the other dimension and make that also 400px; use the image's clipping path if it has one to erase the image's background; save for web as jpg, appending "-400" to the end of filename (but before the ".jpg"); set size to 115 and save for web, appending "-115" to the name; set size to 80 and save for web, appending "-80" to the name.