I am looking to be able to control external relays from RS485 outputs to trigger motors or solenoids.

I am not sure about where to start with this, I take it that I will need a RS485 to relay driver board to achieve this, but I am not sure about how to do this using MIPS SDK and C#.

Can anybody point me in the right direction?

The MIP SDK does not have any functionality for RS485 or similar. Once you can do this from you C# code you will be able to do it also in a MIP SDK based integration, both standalone or plugin.

So my advise on RS485 would be to search in other resources or forums..

I hope it makes sense.