All my pictures hit 400kb. How can I reduce the size without risking too much quality? I see many high-res, detailed pictures uploaded so I know it's possible. :)

For me at least compressing images in photoshop itself looses too much image quality. Usually I will save as a jpeg and then will use an online photo compressor. http://compressjpeg.com Is my favorite right now. Just upload your file and then click the thumbnail and you can adjust the compression amount. I have found it keeps the quality better than just compressing in my art program. Good luck!

Can you resize it that way? Most of the pictures I use start out as 1000 x 1000 at the minimum. Can you shrink the size adequately enough from there? What do you recommend?

I always use http://resizeimage.net/ her you can resize, shrink and turn your picture to a jpg all in one time. It has always worked for me ^^