The 19rnd SP01 mag hangs out the bottom..it uses a basepad to cover the 1/2 or so that extends past the bottom of the gun. It will fit the same way in your 75 stainless..
the SP01 and 75b mags are interchangeable.
as for night sights..there are couple of variants that fit the CZ75b dovetail. the sights themselves are around $50-$60. not sure how much it would cost to install..but it is pretty easy to do your self..