Differential signalling help
you may consider this [on-line calculator][1] to get you started (am sure there are many more other good articles explaining this). Yes the differential impedance should be of the order of 100 Ohms. Other considerations, well, try to keep the lengths equal as suggested, and as short as possible, without obstacles or vias changing layers. If its all on the same PCB then you can try keeping the connections as short as possible. If its board-to-board then you'll have more trouble doing that and more carefull consideration to be given. Hope this helps ...
So the main difference between is that the coupled microstrip is differential, the microstrip is the basic transmission line (surface conductor and ground plane), whilst the embedded microstrip is an embedded-into-the-dielectric conductor and a ground plane. Please refer to the right side of the article explaining the different geometries, its all there ...
[1]: https://www.eeweb.com/tools/edge-coupled-microstrip-impedance