I have no skills in making sketches.
There are no parts that dictate anything ,ok the barrel length but the rest have to be made or adjusted to my needs.
Yes, the parts do determine the architecture. The barrel, and more specifically, breechplug determines the location of the lock. The lock, and more specifically, the sear bar determines the location of the trigger. The location of the trigger determines the LOP on a rifle, or the length and diameter of the wrist and handgrip (reach) on a pistol. In addition, the style of the components will determine the final look of the finished gun.
And while the rear finial of the triggerguard can be bent, it still determines the diameter and reach or LOP, if you will, of the pistol.
IMHO, your components need to be finished prior to layout and assembly of your components, otherwise, the result of your hard work will look and feel like a frankenpistol of mismathced parts. IMHO, James Turpin's "Building Muzzleloading Pistols" describes what is necessary to build a quality ML pistol.
Good luck and God Bless,
J.D.