Are these files on a hard drive attached to the Mac Plus? Otherwise, you're going to need a way to get them off the 800K disk and the only way to do that is with another old Mac. An old inexpensive Mac Classic would solve a number of your problems. Your disks are likely fine, not being affected by the parts of the Plus which presumably caught fire.
If the files are on a hard drive, you're going to need a way to get them off the drive using a SCSI converter of some sort.
Theoretically, TextEdit in OSX should open both MacWrite and Word 4 documents as RTF files. However you will have to open them via the File command, rather than double-clicking the file or dragging it onto the application icon.
If not, you still need to get the files into your iMac. Once that happens you can use
Mini vMac, the best option for this purpose, to directly edit the files in the Mac Plus environment, or export them into your iMac.
