Hi Macintoshguy1984,
I, too, shall repeat what the others have said.
Get yourself any PCI Mac before the B&W G3, or indeed, any Mac that has an EtherNet card. They aren't expensive (well, shipping might be). This machine will form a bridge between the G4 and the Plus. Join the G4 and the other mac via a 10baseT switch. I'm not exactly sure which exact cable you'll join the Plus with the other Mac with. Others on this site will give you the exact cable. All of my Macs have ADB.
Sneakernet (walking around with removable media) is probably the easiest option. I wouldn't recommend Zip disks. The disks are well built but finding reliable drives that work are becoming harder to find.
Instead of Zip-drives, I suggest that you invest in SCSI. You'll need a SCSI-card (preferably with 25-pin external port, but one with a 68-pin LVD/SE port should do). You'll need an external hard-drive with a two SCSI ports. You'll need the appropriate SCSI cables between the hard-drive and both the Mac Plus and the G4. The Mac Plus has a 25-pin SCSI port, which is why I recommended that you look for a SCSI card with a 25-pin external port. You'll only need one 25-pin to 50-pin centronics SCSI cable then. You'll also need a 50-pin SCSI terminator too. SCSI busses require to be terminated.
SCSI is far and away the most flexible and long-running (from the perspective of old Macs) of busses available on the Mac. All Macs bar the first two (which can actually be considered as beta-versions to the Mac Plus — the first proper Mac) can either take SCSI or have SCSI built-in. There are those that will say that Apple botched SCSI on most of their Macs and while this is true in the sense that it ran slower than it could have, all of these Macs still can take SCSI devices.
Once you have SCSI, you can add more SCSI devices onto the SCSI-chain. The aforementioned Zip-drive is very useful (when it works), an external CD-ROM drive (and burner for your G4), scanner etc. Do be warned that SCSI becomes quite complicated quite quickly on account of the number of cables, evolving standards and so on, but I certainly will be happy to answer any questions that you may have. Just avoid HVD...