A Hassy fits in your hand like no other MF single reflex camera. You won’t be disappointed. Go for it. I have a C/M. Never had a need for interchangeable screens. Also have a 2000 FCM, will use until its premature unfixable death. The screen should be just fine for general photography.
That is going way too far, everyone is different. Haselblad hardly fits so well. It might for some individuals, but just as well can feel awkward too. I only say this because having handled all MF SLRs but Rolleiflex 66SL, things are not all roses In handling department.
if you want 6x6 SLR try some choices before plunging into 2k+ investment. For the little info provided this may or may not be a good deal. 500c is long in the tooth, lenses - Which ones? Which magazine does it come with? Can you return it? The latter because you may be unpleasantly surprised, or feel underwhelmed, but also very happy.
For metering you got handheld meter as a choice unless you spend at least 400-500 on PME finder.
weight with Hasselblad is another trap, body is lighter than most in that size, but put on a lens and things may surprise you, of course depending which lens. With old C 80 things are re rather light and compact, with several other lenses it’s in my view worse than most competition.
keep in mind you have a great 645 camera, you are going larger, heavier and far more expensive. Square is a nice format, cropping 645 into square is obviously not ideal.
look into Bronica EC, body is larger and heavier than H, but with lens things get turned on their head.
look into Bronica SQA, my second alternate suggestion.
and may I suggest Mamiya 330? A TLR but square and swell.
