I know the Greek historian Polybius and his analysis of the early Roman republic played a big role.

Polybius saw contemporary Greek states as being caught in an unstable cycle of democracy/mob rule, aristocracy/oligarchy, and monarchy/tyranny, and thought the Romans had escaped this cycle by combining elements of all three in equilibrium. This influenced the concept of balance of powers in the US constitution.

Some of them were pretty well read-up on political theory and historical forms of government, which helped them conceptualize how a bee new government my could work. And some of them were seasoned ‘businessmen’ (some of them basically being slaveowners) or local government officials, so they had some practical leadership/management experience. But definitely not all of them.

They also had plans to periodically adjust the condition constitution for the growing needs of the country. But they were also very wary about foreign manipulation and domestic populism derailing the county. So they locked _form~ down the requirements for amendments pretty tightly. And that has arguably crimped political adaptation over the last few centuries.

Plus they didn’t really anticipate the huge growth in the population or the country’s future needs for the next could couple of centuries. But that’s a hard feat to accomplish.

Edit: curse you autocorrect!

If I recall my early American history, some of what they based their first sets of laws on was derived from those of the Iroquois/Haudenasaunee Confederacy.