If you were looking to do a bit more upgrading, might I suggest getting a SCSI kit for your Blizzard card and using that instead of the Squirrel? It'll be a lot faster, and will free up the PCMCIA slot for a network card. As you pointed out, it will only accept 16-bit cards, but there are plenty of them around. Besides, the network will be less of a bottleneck than SCSI over the PCMCIA interface.
I've never tried a network card over USB, but it's probably the easiest of your options, provided you can find one that works. Is there much extra overhead for running a network adaptor over USB, does anyone know?