Welcome to our little corner of the world snakeknuckles . Disclaimer: Any advice given comes with no waranty but is the best we know. There is a lot we don't know! However, the price is right.
Hard wood or soft wood? Full dimension or nominal?
Circles are great but they assume the tree is a perfect cylinder. Allow extra trees or diameter for loss from bows, sweeps and other defect. What ever you cut will be better than anything you can buy.
If I were cutting conifer I'd pick my biggest and nicest logs to cut the 16"s. And I'd cut them pretty close to first. And I'd cut them free of heart center (FHOC) If a timber has heart center in it, it will crack. 2" out of the center and side boards. Fall back to 1" to maximize yield. The reason they box the heart in timbers and railroad ties is to lessen warp and twist, but they are going to crack.
For a real quick SWAG of what you'd need, calculate the total board footage needed for the structure and use that against gross log scale. You should have at least a 20% over run but that depends on the amount of taper in the logs and defect. Cutting just certain sizes is sometimes wasteful of a log. Example: On smaller logs I like to open a log with a 4" face to maximize yield but 1 x 4's aren't on your cut list.
If I'm cutting 2" dimension wood and opened a 6" face on the next cut I might find it has a 2", 3" or a 4" board after the 2 x 6. With specific sizes required you get into a step function situation.
Sounds to me like Kirk knows about cutting 8 x 8's
