Hi Daniel,
Mathematical for signal processing and dynamical system are essential basis. I also recommend that you have a good vision of the different approaches (biophysical, phenomenological, data driven, etc…) and on different scales (sub-cellular, networks, neural mass, neural field, neuro-glia interaction, etc…). And good programming skills will save you a lot of time…
A good ability to evaluate the possible interpretation of the results, the meaning of making models, and ethical/epistemological questions, are also more than welcome.
Good luck !
Damien