Lens are a very personal thing. For street photography a focal length of 24mm to 50mm is the most useful, followed by a short telephoto.
If I had the Leica CL then I would have two lens, the 23mm f/2 Summicron which gives a field of view of 35mm, and the Leica APO-Macro-Elmarit-TL 60mm giving a 90mm field of view.
So now for studio work.
The Hasselblad X series lens light up is still being expanded upon but there are two portrait lens that interest me, the 90mm f/3.2 giving a field of view of around 70mm equivalent for 35mm, which is a little short for head shots, and the 135mm f/2.8 which gives a field of view of 105mm for 35mm format.
With medium format and 50 MP giving a lot of cropping potential it would be tempting to go with the 90mm and cropping a little for headshots, but it depends on how much room you have in your studio and your budget. The longer lens is £1100 more a big step.
I would go for the 90mm and make it work.