Hi, Tom. I hope that I can save you some money by suggesting that you have a qualified structural engineer do the design for you on both this and your second question. It may not seem like it now, but when you have problems in the future, it will be much more expensive to repair.
In no way am I suggesting that you can't do the construction yourself, but the design work such as calculating loads, needs to be done by a pro. Also note that on any of the home shows on TV, the pro builders like Ryley work to a pro's design. Also, since the engineers make a living designing, they know the latest and greatest ways to solve problems. The peace of mind in knowing that it's done right is worth a lot.
One suggestion--if you live near a school (college or university) with an architecture program, you might call them and ask if they have someone still in school but far along in the program that would be willing to help you out for a price.