There is a handy guide in my sig for your reference.
(I'll be updating it soon with LocalTalk info.)
What "other ethernet enabled Macs" are they? You have two choice: A LocalTalk network or an all-ethernet Network.
The SE/30 can get an ethernet card, a LocalTalk to PhoneNet adaptor, or a SCSI to Ethernet adaptor, as can the Classic II. The Plus can get a SCSI to Ethernet or LocalTalk to Ethernet.
I would just get four DIN-8 to LocalTalk adaptors, two 120ohm terminating resistors, some telephone wire, and hook up all the machines that can can do LocalTalk to each other. One machine will have to be the gateway between LocalTalk and Ethernet: I don't know if OS X can do LocalTalk, but you can't have LocalTalk and Ethernet on the same computer active. But you can just switch between them quickly on the gateway machine -- just leave the TCP/IP (or Network if you use MacTCP), AppleTalk and Chooser windows open (WindowShade may help) and flick between the two network types.
The benefit is that your machines with System 6 won't need to do MacTCP and Ethernet work, but it's not that hard because others have done the legwork for you. But the major benefit is PhoneNet connectors are DIRT cheap. Type "phonenet" into eBay and marvel.
Here's the problem with USB floppy drives: They only support PC 720KB and 1.44MB sizes. You can only use 720KB disks if you have a SuperDrive and PC Exchange (7.1 MAY be able to do it, but better is 7.5). Also, floppies are notoriously unreliable, fickle and tiresome. Don't bother with Zip disks either -- trust me, you can use LocalTalk (even ethernet, as I have done) on a single 800K boot floppy (but two for better work, see my Guide).
Once you use networking reliably, you won't bother with floppies. Trust me.
(I'll be updating it soon with LocalTalk info.)
What "other ethernet enabled Macs" are they? You have two choice: A LocalTalk network or an all-ethernet Network.
The SE/30 can get an ethernet card, a LocalTalk to PhoneNet adaptor, or a SCSI to Ethernet adaptor, as can the Classic II. The Plus can get a SCSI to Ethernet or LocalTalk to Ethernet.
I would just get four DIN-8 to LocalTalk adaptors, two 120ohm terminating resistors, some telephone wire, and hook up all the machines that can can do LocalTalk to each other. One machine will have to be the gateway between LocalTalk and Ethernet: I don't know if OS X can do LocalTalk, but you can't have LocalTalk and Ethernet on the same computer active. But you can just switch between them quickly on the gateway machine -- just leave the TCP/IP (or Network if you use MacTCP), AppleTalk and Chooser windows open (WindowShade may help) and flick between the two network types.
The benefit is that your machines with System 6 won't need to do MacTCP and Ethernet work, but it's not that hard because others have done the legwork for you. But the major benefit is PhoneNet connectors are DIRT cheap. Type "phonenet" into eBay and marvel.
Here's the problem with USB floppy drives: They only support PC 720KB and 1.44MB sizes. You can only use 720KB disks if you have a SuperDrive and PC Exchange (7.1 MAY be able to do it, but better is 7.5). Also, floppies are notoriously unreliable, fickle and tiresome. Don't bother with Zip disks either -- trust me, you can use LocalTalk (even ethernet, as I have done) on a single 800K boot floppy (but two for better work, see my Guide).
Once you use networking reliably, you won't bother with floppies. Trust me.