Would separate libraries be needed for EXOS and EXDOS, depending on whether you were using tape or disk storage?

Only for loading, and saving files you do not need, EXOS handles this, and route to the default "device", if you have EXDOS, than EXDOS is the default, in basic EP config TAPE is the default.

ISDOS is stored on disk and is some kind of bridge between IS-BASIC and EXDOS.

No, it is not a "bridge", but a CP/M.
ISDOS is originally released on disk, which is a CP/M.
Later, ISDOS is contained in ROM, which was included in unofficially EXDOS versions (32k ROM).

I didn't have a disk drive when I owned an Enterprise, so I'm a little confused about the differences between EXOS, EXDOS and ISDOS.

I'm currently exploring the possibility of adding Enterprise support to the ACK compiler, so I need at least a basic understanding of all three before going any further.

From what I can gather, EXOS is stored on ROM and is available on all Enterprise machines. It handles video, audio, tape loading/saving, i/o etc. and can be accessed from IS-BASIC or machine code.

EXDOS is stored on ROM on Enterprise disk drives and handles disk control, a little like MS-DOS.

ISDOS is stored on disk and is some kind of bridge between IS-BASIC and EXDOS.

CP/M and MSX-DOS also seem to be supported, but I'm not sure how or to what extent.

Do I have any of this right? Do I have anything wrong or something missing?

EXOS 2.1 esetén:
m bfcc
eredménye:
>BFCC  00 00 FF 03 1E 00 00 00  :........
majd az első 0-át írd át nem 00-ra, és enter

EXOS 2.0 esetén:
m BFD0
eredményét nem néztem meg
és itt is az első 0-át írd át nem 00-ra, és enter

Cool
I think text on those screens should be translated also, i will share that part of the source with you, as i remember it contains all other needed texts.