It may be a good idea to reconsider building a house. In many areas of the United States, it's currently much cheaper to buy an existing home than to build a new home. There are MANY homes for sale in most places, so selection is generally good. It is also MUCH easier to buy an existing home than to build a home!
If anyone in the OP's family has allergy problems or asthma, it would be an excellent idea to build a "healthy house". Healthy homes are designed to provide an ultra healthy indoor environment. These kind of homes are good for everyone, but are really helpful for folks with certain health issues. John Bower has written a bunch of books on this subject. There are other good books on the subject available as well.
On the garage, I like a detached garage with a roof connecting the garage to the house. A detached garage is usually safer. Cars will occasionally catch on fire while parked. Carbon Monoxide and other fumes and odors from the cars are less likely to enter the home from a detached garage. A covered walkway, or breeze way, connecting the house and garage would be ideal in many areas. In cold northern climates, an attached garage might be a better plan.
I like outdoor living areas on a country home. In bug and pesky insect country, a screened in porch is ideal. A detached gazebo is another option.
Someone mentioned earlier about allowing an extra 10-15% for unexpected expenses. That may not be enough. It depends on how good a person is at planning and budgeting!
A good architect is well worth the cost of their fee. They can point out problems and offer suggestions on how to improve a design. It's a good idea to know what you want and can afford BEFORE going to see them though! Depending on the situation, an interior decorator can also be helpful at times.
If the OP wanted to build a smaller home, he could build a detached "guest house" for his company. Depending on the company, it may be nice to have them in another building!:laughing: The guest house could also be converted into a small rental home if desired at a later date. Some folks will also use recreational vehicles (campers) for company. If that's done, some RV utility hook-ups should be incorporated into the design of the house.