You are on the right pathway, my man. You would not believe how many people do not consider the "over-building the neighborhood" thing. Now I won't be able to cover all the bases here, but given time, and considering some of the brain power on this site, you should get most of what you need.
First, some of this depends on your goals. Are you in love with your existing house and it's locations? Does your kids think it is great, or worse yet, your wife? You get the picture. If you want to stay where you are.......that has a "real" value. That value you have to put on the project, especially if in reality you really don't want to move. I mean, when you croak, who cares? If this is the case, then you can free yourself up a little as to whether you are over building the neighborhood.
Another issue, will the existing structure handle the new additions? There is a point when you love the location but not t