Well, I'd get it all up and running and see if you really feel a G3 upgrade is needed.
In many cases, if you're sharing a Cable/DSL conenction, and if you turn off all the unnecessary extensions that you don't need (Speech, ColorSync, FileSharing, etc.) and bump up the memory allocated to the...
UPDATE: Hey Andy, I just checked my closest and blam! I have a spare 10baseT PCI Ethernet card for you. I also have a spare Mac OS 8.0 CD as well.
Got a DVD that you no longer like/watch anymore? If so, we could just work a swap or something. That way it won't cost you anything....let me know...
If you look on the spec sheet, the last "supported" OS by Apple for that machine is only system 8.0. That means that you shoulkd really just run that, or possibly 8.1 (if you can). There may be some hardware related drawback that will not allow it to run 8.5 effectively.
Scan eBay for system...