Maybe that 386 would have been better used as the file server
You don't mention what sort of network software you were running at that time; I'd guess from the way one file copy brought the server to its knees that it probably wasn't Netware.
You don't tell us much about the actual network. Since its 1990 the network is likely to be at best 10BaseT running half duplex through hubs using Cat3 phone wire. (It could even be something earlier than 10BaseT such as Starlan). This might generate problems if you've got a lot of people trying to share it, because of collisions -- an individual user (the person setting this thing up) would see decent performance but a sales floor's worth might collapse the thing. Even so, if you could monitor the traffic you'd be surprised at just how little you were loading the network.