Thin clients using ACP Thinmanager and MS Terminal Services, works great for WW. Upfront cost is a lot more since servers are required and you need licenses for Thinmanager and Terminal Services but, in the long run, costs less. Thin client bricks have no hard drive, no fans, and therefore no moving parts, great for harsh industrial applications. Typically you can run 6 to 10 clients on one server.
We install 7 servers for an average size plant. 1 domain server, 2 redundant Thinservers, 2 redundant I/O servers, and 2 redundant SQL servers.
At a minimum, I would suggest 2 Thinservers and 2 I/O servers. This setup will easily run 10 to 15 clients. Add 2 SQL servers to store historical data. If you need more clients than the 2 servers can handle, just add another Thinserver and licenses.