Hi Thorsten,
When you select the "Configure Storage Disks" option, NASLite does not blindly format all disks. It asks you which one (1,2,3 or 4), and then asks for a confimation. In other words, you can select which drive you wish to format without affecting the other drives.
In addition, since NASLite essentially reconfigures the system on reboot, swapping drives will not cause any problems whatsoever as long as the actual swapping is done in the power-off state (common sense here

)
That out of the way, i don't see any problem with what you are planning to do in all 3 of your scenarios.
Hope this answers your question.