@bghazzal If you're doing exclusively macro, I think a dedicated macro is the way to go (maybe Zeiss Touit 50mm - 75mm FF equivalent), plus a CMC-2 (easier to work with) and CMC-1 (more magnification) - or equivalents. The 16-50mm would give more flexibility if you use a wet wide lens and close up lenses, but it's very pedestrian for close focusing on its own, unlike the FF 20-70mm or Olympus' 12-40/45 lenses. The 90 macro on APS-c is a 135mm FF equivalent - a bit unwieldy and tight with its narrow angle of view - probably not good for BW.
I have a FF A7c and a 90 macro. Had and sold the Sony 50 macro. Looking to try a Zeiss Touit 50 macro on an APS-c body in the future. Probably the A6700. I traveled with the FF Sony 50 macro, which worked okay with the A7c in terms of locking on and tracking for general photos. The combo did not work well for me with BW. I was autofocusing, locking and tracking - but the photographer - or the combo - was too slow. Manual focusing with both the Sony and Zeiss may be a chore with their relatively long throws (turn, turn, turn). I've seen pretty good FF 90 macro BW, but I haven't tried BW with that combo. You'd think, living in Hawaii, I would have more opportunities to do BW, but my time in the water is limited by personal circumstances.