Is replacement of this motor a complicated job and is there a high failure rate for it?

Also, I need to replace the shift detent cam. Should I also replace bearings and such?

i dont know but i hate the darn thing, first time the brake released it scared the @#$%& out of me.... can the brake be used if this option
is disengaged???

I haven't replaced any of the things you mentioned, but it can't be that difficult. I suggest you get the factory shop manuals for the car. They will be a big help.
Yes, the brake can be released manually. There is a small lever under the dash right next to the vacuum release. Just pull on it. It takes some effort but that will release the emerg. brake.