You will find lots of examples in the wiki http://wiki.linuxmce.org/index.php/Category:User_Setups
But basically, you need one core (I would go for a separate core, as you have 4 places you want to play media), and 4 MDs. Alternatively you could combine one MD and the Core into a Hybrid, but I'm not sure I would recommend that here.
For the satellite you have two options. Either you can have LMCE control the decoder using IR, and just connect the decoder to the TV directly. This setup won't allow you to record anything though.
Second option is to have a TV-card in your MD or Core. What card and how depends on the satellite broadcast. If you can get a tv-card that decodes your particular satellite broadcast using a CAM/CI combination, I would go for that. If not, you need some device like the HD PVR that encodes the output from the sat. decoder and passes that to LMCE.
Also note that using the second option you can keep all your sat.decoders and core in one place (a cupboard for instance), while only having the MDs in each room.
For the bathroom, I'd choose a squeezebox or a use squeezeslave on the core.