My understanding is that gingerbread destined for houses is made from recipes different than when making cookies, etc. The "construction grade" produces a much stiffer, stronger bread, able to withstand the rigors of house building.
Keep in mind, too, that if you make shapes before baking you are likely to run into problems with mismatching. That is, two squares, for instance, that start off the same may not shrink or expand the same, will not have true corners, etc. One reason so much Royal Icing is used in gingerbread contruction is to fill-in those mis-matches, as well as to serve as a mortar to bind pieces together.
For windows, make appropriate stencils. Melt hard candies and pour them into the molds.
Most Christmas tree lights, even the minis, are too big for gingerbread houses. You'd be better off with a series of LEDs---providing the exhibit rules allow them at all.
Were it me, I'd start by experimenting with a simple 4-walls & a roof house, to develop a feel for working with the gingerbread and decorating techniques. Then move on to something more complex.