I think you can add the sirius and blue tooth to your car aftermarket. Try www.bsw.com
I think they sell kits for your car. As for the nav screen, if you buy a factory nav unit and have a knowledgeable stereo shop install it, you shouldn't have a problem.
On the E39, if you don't have factory nav screen, and want a factory nav screen, it is a pain in the ass because the vents are located lower in the non-nav dashboards. So, if you have an E39 and want nav, you have a choice of a portable nav system or a Flip down.