Internal HDD's jumbled up, on SATA ports?

If you physically check your Motherboard SATA ports each one should have a number assigned, which would normally match the number you see on your image as the Drive Number.

It's a simple (or should be ), open the case of a desktop and connect the SATA cables in such a way to allocate the drive numbers in any way you wish, will it make a difference, probably not, but as the BIOS is likely to poll the Sata Ports in Order, Most users take the time to order the cables, as it can help ID a drive to check it's physical connection if it stops working, (and we're all a bit OCD )
The system BIOS screen may show the drive connections if you wish to check that the system agrees with windows

Drive letters are actually assigned to partitions rather than drives ( a partition can cover a complete drive), and can be changed from the screen you show - obviously if you wish to allocate a letter that is already in use you need to either assign another letter or unassign the existing letter as you cannot have two partitions with the same letter

As for the assigning of disk 2 to a removable drive this may not always be possible due to historical reasons which tend to require removable drives to have their own SATA ports on the M/B, but it should be worth a try

Drive letters can be assigned as you wish, drive numbers are set by the physical location of the connections on the motherboard,

When assigning Drive letters lets say that you wished to assign the D: drive to to a partition, you would need to first assign the current D drive to say Z, and then the new drive to D