For wide angles, if I were you I'd just get the 50mm II and stitch if you're purchasing. I've never shot with it but all the reviews and anecdotal evidence on forum posts suggest that it's great. It will work well on the 50c and the 100c you've got coming later.
Digital Transitions did a
100mp 35mm test with the 35mm using a Hasselblad H5x and IQ3 100mp, which would probably approximate what performance you would expect to see on the H6D-100c you have on order. The 35mm didn't perform well compared the Phase One 35mm (which was recently redesigned and re-released as one of the first of their blue ring lenses). Granted it's only a few pictures with one copy (and performance would be better on the cropped 50c vs the 100c), etc etc etc but the results match up with what others say about the lens.
As others have stated, the 24mm and 28mm HCD do not cover the full image circle of the H6D-100c and I haven't seen any test shots with either of these on the 100c. They may very well be usable and produce great 70-90mp crops from the 100mp sensor, but I personally wouldn't want to
buy into this combo if the 100c was my end goal until I see the 24mm and 28mm on the 100c in practice. I'm very anxious to see how the HCD lenses perform myself on the 100c as I have the 28mm and 35-90mm already. Purchasing either of these now for the 50c with the intent to use them on the H6D-100c may not be the best option. If I were you and you wanted to do something other than stitch with the 50mm II, I'd look into maybe renting the 24mm or 28mm for use with the H6D-50c for your trip if you can.