holmes4:
While you will start with a 6v supply the voltage will soon drop at which point you will have problems. I thing you would do much better with a 9V supply and one or more voltage regulators ( the system used on the UNO) for example.
If by "9V supply" you mean a standard 9V battery; that won't not have enough charge capacity to run two motors and eight LEDs for long, especially with the extra power losses from voltage regulators. Instead I suggest using six AAA batteries (with appropriate voltage regulators). There are battery holders readily avaiable for this configuration.