The Arduino is a sensible choice for interacting with the hardware. I'm not sure whether you would be using ordinary DC motors, or stepper motors, or servos. Servos would be very convenient in many ways because the contain their own drive circuits, but you would need to go into your requirements for the 360 degree motion in more detail to know whether a servo was a sensible choice for that.
For driving DC motors or a solenoid you would need a driver circuit. It's possible to get Arduino shields which plug onto a standard Arduino shaped board to drive two motors or motor + solenoid but you would need to check the electrical specs to see whether these were up to the job of driving your devices. It's also possible to get Arduino clones with the motor drive circuits integrated onto the main board and if you only need a small current (say under 1A) that might offer a smaller and cheaper solution. You can also get more general drivers which need to be mounted separately and would be wired to the Arduino. You would probably need something like this for larger motors or if you wanted to drive more than two motors.
In order to provide remote access to the control interface you *could* use RDB into a windows desktop but a cleaner solution would be to create a web app on the PC which uses the serial connection to send commands to the Arduino and get status info back from it, so that you can access the UI remotely from any web browser without needing the hassle and security vulnerabilities of desktop access. This would make it possible to access the UI from smart phones, tablets etc and not just devices with RDP client support.
Would running PI with WIFI (connectivity to far for hardwired connection) ... while the adruino is connected as a motor controller work? I dont need the RDP app I'm just not 100% certain on all my options. My idea is to connect via a smart phone and monitor/move the mill. Also, I see that the PI has a 5mp camera available. This would allow me to see what is going on as well, provided the PI had enough power to handle the tasks.
I saw an individual on you tube made an RC car that was operated from his phone, and he used the camera on pi to see where his remote car was going. Seems like a powerful little microchip. I think the potential would be great if I could get it connected to the adruino.
So to clarify, If there is a wireless connection available to my PI, then in theory there is a way I could connect to it and stream video from it, send it commands, or execute programs>?