It also depends on the tool you use for upsizing. Tools such as Pro Photo Zoom, QImage, ImageMagick, ON1 Resize will give better results than the bicubic method of Photoshop. If you use the latter, you might consider looking into ImageMagick (which is free). There is a very useful thread
in the forums about it including some scripts you can use right away.
Besides that, I would definitely do capture sharpening, chromatic aberration handling, lens corrections and noise reduction prior to enlarging. The output sharpening and the creative sharpening would be done after the upscaling. Some other adjustments such as general tonal controls don't matter much. If you use local contrast enhancements or clarity, it might be better to do them after upscaling.
Hope this helps.