Is it true I can only use the SCSI address 5 or 6?
You can use any ID which is not in use by another device. The host adapter usually has ID 7, so you can use IDs 0 - 6 for your devices.
There might be limitations on how the ID is configured on the drive.
The IOMega tool does not see the drive and not sure if I need to use ZIPMount_12.lha? I saw a message about Mountlist DEVS:Dosdrivers
Yes, you have to make a mount file in Devs/DosDrivers.
The ZIPMount archive probably contains a mount file for 100 MB ZIP disks. You have to change it to the size of your cartridges.