Methods for telling gender at a week old are not very accurate. You will have a 50% chance with these methods. The best bet is to buy sexlinked pullets or purchase as pullets from a hatchery or feed store. That is 95 to 99% accurate
Nice idea for controlling the heat coming from a heat lamp. Make sure the the voltage regulator is rated for the power of the light. Make sure it does not over heat
The MHP and the Premier 1 brooder plate are good choices for brooding outside. The Brinsea is not rated to go to freezing temps. The Premier 1 and the MHP can