I'd like to know if a sentence like the following is grammatically correct and, if not, how it can be written.
The many friends you have, the more important you are.
This idiomatic construction compares two values, of which one increases or decreases proportionately with increases or decreases in the other. It therefore requires two comparative expressions:
The more beer you drink, the drunker you get.
The more friends you have, the more important you are.
A positive expression such as many cannot be employed in this construction. Perhaps you mean what can be expressed in a conditional construction:
If you drink much beer you will get drunker [implied: than if you drink only a little].
If you have many friends you will be more important [implied: than if you have only a few].