There is a lot of internet hype getting parroted here.
Yeah, on exposures longer than maybe 1/30 there is some risk you could let go of the botton before the exposure is completed.
If know this, and keep your finger on the release it's not an issue. It's not like releasing immediately, whatever that might, be accomplishes anythng else, since the mirror is up and stays there until you advance.
As for mirror slap, make pictures and don't worry about it. I've made high magnification macro shots with and without pre-releasing the mirror, there is no noticable difference in the images. Mirror slap isn't an issue on any exposure you can hand hold, whatever movement it could cause will be far outweighed by your body's movement.
The lens's shutter needs to be cocked before dismounting or mounting. While it's possible to release the shutter on an unmounted lens accidentally, it happens only rarely. If/when it does, just dig a coin out of your pocket, or the edge of a film spool, or whatever else and cock it.
RB's are heavier and make bigger negs, Hasselblads are lighter and make square negs. Both have great lenses and have made stunningly great pictures.
Pretty much all cameras have one particular "feature" or another that you need to be mindful of to operate successfully.