I'd put all the outlets in the walls at table height. Who wants to bend over all the time to plug in a cord? If you know where your long arm will be located, you could ask to have a power strip installed on that wall, too. Extra plus of that is that it is much easier to clean if the power supplies and cords are not littering the floor.
Don't forget to have good overhead lighting installed where your long arm will be. It makes a difference!