I am planning a project whereas a Diavolino will be installed inside of a PC.

1. Data will be sent from the PC serial port to the Diavolino ( via a MAX232 ). Do I need to think about RTS/CTS?

2. I plan to power the Diavolino from the PC +5v rail. The Diavolino will be powered after the PC and apps are running, so I don't need to put a load on that rail. Is there anything else I should consider?

Thanks

Data will be sent from the PC serial port to the Diavolino ( via a MAX232 ). Do I need to think about RTS/CTS?

If you're sending just data, then no. RX and TX (and a common ground, of course) are all you need.

On the other hand, if you want to reprogram the Diavolino, you'll need a way to reset it to re-engage the bootloader, which is where the other lines come in. You could run a pair of physical wires to an external reset button to do this as well.

I plan to power the Diavolino from the PC +5v rail. The Diavolino will be powered after the PC and apps are running, so I don't need to put a load on that rail. Is there anything else I should consider?

I'm not sure what you mean by "put a load on that rail" in this case. However, the Diavolino itself draws rather negligible power (typically < 20 mA), and should work fine on the 5 V rail inside the PC.

Thanks for the quick reply.
The Diavolino will be processing data sent from an application on the PC. Any re-programming of the Diavolino will be done stand-alone.

The ATX power supply needs a load on the +5v rail to function correctly.