I've just started playing with WHDLoad on my
CD32+SX-1. Assuming I can actually get something installed correctly (IE, my original disks aren't corrupt) my 4Mb of FAST is plenty. Flashback, EOB2, and Populous work splendidly, but there are OS Swaps. Not many though.
To get absolutely everything working, you'll need 1.3, 2.0, and 3.1 ROM images and most installs need an XFD package with supplementary libs.