Medium format is different, but not a huge learning curve. Just go with films you know. Overexpose Portra and 400H,
shoot Ektar as rated (maybe a Half stop extra), know how to push Tri-X, etc. you will be just fine. Just know that the FOV
is wider, but the DoF and the "compression" is true to the lens.
For lens, I wanted a 2 lens system with FOV similar to yours. I went with a 60 (35mm equiv) and a 150 (85mm equiv) and
have been very happy. The 60 is a great walk around, landscape, and environmental portrait lens. The 150 is a great
portrait lens and I love it for what it is.
The 645 is a great focal length, but not for hasselblad or Bronica portraits. The way the film feeds makes a 645 a wide
ratio. Can't really flip these WL cameras side ways. It would be fine for environmental portraits... But not better than a
6X6. Stick with the square IMO.
You found the right forum, these guys are great.