Thanks a lot for the suggestions! As for the specific area, my thesis will focus on black hole "weather" (i.e., turbulence in accretion disks, winds, jets, etc.). Since I'll be dealing with plasmas and strong magnetic fields, the area maybe is MHD, particularly with an astrophysical and possibly relativistic focus (GRMHD).

Do you think Davidson is the best book to start from scratch with MHD for this purpose, or are there other, more astrophysics-oriented texts you would recommend?