one Arduino with RS485 and Ethernet shields: does this work? I'm planning to wire a few Arduinos together via RS485, and have one of them act as a hub that collects information from the others and presents it via http on an Ethernet connection. 

For instance an Aduino MKR with ETH shield and 485 shield. Can I expect these to work together? My worry is having 2 shields that potentially need lots of bandwidth, timing issues etc.
Should be no problem.

The ETH shield uses SPI to communicate with a W5500 chip. That chip does most of the network processing for you.

The 485 shield just connects to the UART TX and RX pins. It's just serial communications with a couple of control pins from there on out.

Neither use any pins that the other one uses.