What card to use : Scale and Pump Application

Hello,

I'm trying to make a dispenser that controls a pump using an electrical/pneumatic solenoid for an output to my pump/valve, with input coming from a serial (RS232 Comm) scale.

Basically, I want to set the dispense variable using a num pad and LED display, and then a "GO" button to start the process.

When the scale reaches the dispense variable (7kg eg.) the process stops and the pump/valve close.

What arduino board am I looking for? I feel this is a pretty basic function, but I want a card that'll last a while with repeated use. The most complicated thing I think is the serial communication, but I can get an RS232 to USB adapter for that since I've seen a number of Arduino's have USB ports.

I'll try to answer any questions that will help clarify my requirements.

Thanks in advance for the help!

What arduino board am I looking for?

With very few inputs and very few outputs, any model will work.