For me, 3 optical bays is the minimum. On my system I have two taken by optical drives (blu-ray reader and DVD writer) and the third is occupied by a memory card reader with extra front USB ports (2x USB3 and 4x USB2) and a front eSATA. And that means I don't have space for a front SoundBlaster panel so my wife got that instead. This case certainly delivers on that so I find it acceptable.
Speaking of the internal bays, each 3.5" bay can house two 2.5" drives via an adapter so that provides for a maximum of 12x 2.5" drives.