Congrats!  My family built their own homes all the time and my parents still live in the house they built.  The only advice I can give is... don't skimp!  My parents built their home on the small side even though they had a large lot.  My mom always says they didn't plan to stay there forever.  Now 30something years later and they are still there and they often comment on how the rooms are small.  They even built an additional large family room a few years ago to make it bigger.

The point is, if you are gonna build it, you should make it as big as you can affordably make it so that years down the line you aren't complaining about it :)