how many users could you support?
Back in the day you had six cpu minis with just a couple megs and two-digit megaherz clockrates that could support hundreds of users simultaneously. So a contemporary quad cpu with that memory? Add a few zeros to that number. Probably more than you'd find terminals for. You'd need scads of terminal servers lest the serial handling would become a problem, x86 iron isn't that great there. That sort of thing isn't really cpu-bound, nor memory-bound.
I'd use mutt and alpine to taste. lotus 123? teapot (despite its pointless "upgrade" to cmake, silly developer). wp51? I'd sooner use ws33 (under z80/cp/m emulator, oh yeah), but some editor (vi, pico, nano, ee, you name it--no not emacs you silly bint, we already got us an OS thank you) and troff (groff these days, despite everything, though I hear a non-gn00 version is available these days) would work too. In fact, hosting that was the original killer app for unix. For, oh dear, the lawyers there to write patent applications with. Anyway, even there are a few alternatives that people might prefer and it wouldn't be a problem to provide a good selection, if not all.
The sad fact is that you could do all that and provide perfectly viable productivity suites, that would probably cause sudden upsurges in actual productivity because no distractions, even still provide limited web capability that'd work perfectly well for simple boring fact lookup if fewer sites would insist on adding js without apparent need, but that few people would get the point and thus wouldn't want to work like that. We likes our precioussss clickibunti distractions, yesss we does.
Thus the modern equivalent is the "thin client", which goes a way but preserves the clickibunti. Needs more client and server side oomph to keep going, though.