Is it possible to hide parts of the mesh when I rebuild the topology?
Yes. Hide parts like you normally would. Lets say you are doing a body and want to retopo a hand. Hide everything but the right hand. Make sure your symmetry is on, and start retopologizing. It will build the topology automatically for you on the other side so long as your symmetry is on and the best part is that you can rotate around the visible mesh with local transformations active.
I think of hiding parts without hiding the topology…
Not sure what you mean. If you want to hide parts of the mesh, you are going to hide parts of the topology. If you want to view the progression of your overall topology flow, then just press “A” to switch back and forth between the adaptive skin preview and the topology working area. Set your skin to the lowest level in the Tool>Adaptive Skin menu to view exactly what your topology will look like and hit Shift+F to switch between your frame wires and view the topology better. This will allow you to see the new topology of the whole model at once while working on the topology in a localized area of hidden parts from the original concept sculpt.
While you are doing retopology you can hide parts of the new topology but not the base mesh. Whatever portion of the base mesh was visible when you start retopology, that’s what must remain visible for the duration of the retopology session.