Read “What do I do first”. Make sure all the construction is complete for each room. Paint all your ceilings. If possible, hold off on adding the roofing (shingles) or outside fascia and wait to install the stairways. Do install windows but you may want to wait on gluing in the doors. Also wait on installing flooring, any wall coverings, wainscoting or base and crown moldings. After you have run your flat tapewire and provided a point of connection for all of the ceiling lights, fans, sconces, you can lay the flooring, glue in the doorways, and install the stairs.
It is not too late to add electricity if you have already completed total assemble. You just have to be a little more creative in how the wires get from point A to point B and you will find using the Kynar hook-up wire becomes easier to use than the flat tapewire. As I mention in my booklet: “Learning how to electrify your dollhouse is not the problem—it is how to run and conceal all the wires”.