What happens if there are 2 bootable drives with the same priority?
The drive which comes first in the config list will boot. Check boot options in the early startup menu. The left list shows the order. The topmost drive is the default boot drive.
The only way to change the order of the config list is to connect the controller to a different expansion slot (in Amigas which have multiple expansion slots, i.e. Zorro2 / Zorro3).
I'm guessing that my HD should have a slightly higher priority of 1
If you are happy with both having prio 0, you can leave it alone. You only have to change it if you want to change the boot drive.
if I change this in HDToolbox, will I lose data on the drive?
No, you won't leave anything. HDToolbox would warn you before it writes to the disk, if you'd loose something. If HDToolbox silently quits, everything is ok.
what is the minimum and maximum values, what are 'normal' values for floppies/hard drives, etc.
Minimum is -127 (-128 means not bootable), maximum is +127.
Normal for DF0 = 5, DF1 = -10, DF2 = -20, DF3 = -30, HDD = 0.
If you want to prevent it to boot from floppy, set your HDD to 6 or higher. If you want to boot from every floppy drive, even if a HDD is connected, then set the HDD to -31 or lower.
