Has anyone ever done it? I'd love some input!
YES. Conklin makes an elastomeric paint product. You can get more information on it from their website.
Yes,and with good success get your self a metal to metal primer then top coat with whatever you want.
Sure you can paint the steel siding. The main thing you need to do is get it clean and remove the chalked up paint that is surely there. You will need to use a house wash made for this purpose and a power washer and you may have to wash it twice to get all or most of the chalk off. In most cases you can use an exterior acrylic primer if no chalk is left on the surface but if chalk still remains you will need to use an alkyd metal primer. The finish paint should be an acrylic and either satin, semi-gloss or gloss depending on your taste and remember that 2 coats of finish over the primer will last longer. Your local paint store can help you out with this project.