Here's how I plan to get my //e connected:

I have a Super Serial Card and a b&w Power Macintosh G3. I've got the G3 configured with OS 10.2.8 such that its serial ports (printer and modem) are open for tty connections. The //e can then run any competent terminal emulation software to login. If I install wget or lynx on the G3, then I can use one of those via the //e.

An Apple IIgs has built-in emulation of the Super Serial Card, (as does the //c, IIRC) so you wouldn't need it for those machines.