Do you have any insight on designing a mid-century fireplace from scratch?

Hubby & I bought this fixer upper and have been acting as GC & designer on other projects. So far all those projects turned out great. BUT THIS seems intimidating mainly because I am not finding much info online on how to go about this.

THE HEARTH IS THROWING ME FOR A LOOP- got any insight on what kind of stone to use?

Are we taking a big risk if we don't hire a designer?

A professional will definitely install the fireplace, run the gas line.

Here are the designs we are leaning toward.

Laverne as Shirley House · More Info

Family Room · More Info

Interior · More Info

How in the world do you cantilever a hearth??? HELP!

Thank you in advance for any insight you have.