dumb newbie question about power supplies

I have just learned the basics of arduino and how it works. I’m going to use it because it works great for a one-off project I have while also allowing me to add things to it later.

My project involves controlling a motor with an h-bridge. I understand basic electronics and have found some great tutorials to make it happen.

Once I set this project up, I would really like to be able to plug it into the wall and not mess with a battery. My motor is 12v with a no-load current of 120mA. I’m not sure how to calculate the full-load current but here is the motor: http://servocity.com/html/60_rpm_precision_gear_motor.html.

I know the arduino can handle 12v and I’ve read a few other threads that said I should power the motor with an external power source. Is it possible to connect USB to power the board AND an external wall adapter to give 12v for the motor? Despite the other threads I found, can I have one external supply for the whole thing?

I have not yet purchased any arduino or component. Where is the best place to find a 12V DC wall adapter for the arduino?

I’m sorry if these questions are stupid. I feel like I did a good amount of research before posting and I’d appreciate any help.

Is it possible to connect USB to power the board AND an external wall adapter to give 12v for the motor?

Yes, see:- http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

I'm not sure how to calculate the full-load current

Just use Ohm's law and the DC resistance of the motor windings. This should be on the data sheet but if not measure it with a good meter.

ya u can use a single supply (preferably 12V one). Make sure u use a large capacitor in parallel with the supply output, the motor consumes a lot of current at the instant it starts and then the current comes low. Else the power surges created may cause the arduino to reset every time the voltage goes low when u turn the motor on.