Do I need to have QuickTime installed to be able to play Safecracker?
Yes, but it is provided on the Safecracker CD.

Will Safecracker work with new QuickTime 3.0?
No. You will have to install a previous version of QuickTime from the Safecracker CD. Do not worry, QuickTime v3 and v2 will peacefully coexist on your system.

Will there be an Amiga version of Safecracker?
Possibly.