The first thing that I would say a state constitution needs in order to be “functional” is three branches of government. Each state needs to have a legislative branch because states need laws to be made. Each state needs the laws to be carried out so they need to have an executive branch. Since they need the laws to be interpreted, they need to have a judicial branch. Without any of these branches, there would be basic governmental functions that could not be carried out.
A second thing that a state constitution needs in order to be functional is some allowance for the government to get revenues for itself. A government cannot function if it does not get any revenue. Therefore the constitution must specify ways in which the government is allowed to get money.
Finally, I would say that a state constitution needs to make provisions for having smaller divisions of government. In other words, a state is likely to be too big to be run from one central location. Instead, the state is going to need to have county and city governments that would ensure that people in all localities could be governed effectively.