Well I don't recommend designing the timber frame structure without calculating all of your joint stresses. You cannot just guess what will be strong enough. The number of pins needed at a joint is determined by the stresses at those joints. A kingpost design especially needs to be sized according to the stresses. This is tension joinery which is the most precarious so it must be designed correctly. Steve Chapell's book explains the calculations, but if you are not an engineer, you may get confused at some points. A lay person can learn this, but it really helps to have someone to go to when you get stuck or have questions. And you absolutely need someone to check your work. As an engineer, I always want someone else to check my work. You can look at the same mistake 10 times and never see it. It always takes a fresh set of eyes to spot some mistakes. I took Steve Chapell's intro course which is a week long. We spend 2 days on design and joint analysis. I was ok with that because I was already comfortable with the math and stress concepts, but for others, they struggled a bit. In truth, you could make the joinery design/stress calculation a several week course. Don't be intimidated though, because once you are comfortable with the basics, other joints are just slight variations on the same calculations. You are calculating resultant loads due to your snow and wind loads (and weights of the structure and any other added weight). Then you are calculating streass and how much shear area you need to handle it, which will lead to the sizing of the joints(mortise and tennons) and the number of pegs using the material properties for the species you want to use.
I am assuming by the way you wrote that you are new to timberframing and have not had a course. Please forgive me that that is wrong as I am just going by the way you wrote and the way you seem to be going about the design. I am a newbie myself but have had an intro course and am comfortable with the joint design and the math.
