Overwhelmed is definitely a common stage. For me, I think some of the stages are:
1. Shear excitement and impatience: after you order the kit, look at pictures on-line, and finally get the kit home
2. Overwhelmed: once you open the kit and see all the parts, the often-wonky instructions & schematics
3. Excitement, impatience and some early gratification: when you dry fit and see the possibilities before you
4. During the build, I experience all kinds of emotions: frustration, elation and amazement
Like Holly said, sometimes you need to walk away, have a nap or beverage, etc. Our minds are unconsciously sorting out the problems and absorbing what the house wants to be when we take a break.