Roughing in the frame is just about as hard as putting in a window or door fame.
Basically the same difference. I am estimating that the opening will be probably in the nature of 4' or less? (About 2 people to sit in, comfortably, because anymore than that, you may as well bring on the kitchen table
Now, you should look at the "bar stools" that you want to use for this, before you start to "hack away" at the wall... Then govern your height requirements to that.
Now will this be a "through" to both sides? Being that your going to have people on one side and on the other? (Kitchen table mode again), or, just from the living room or kitchen? Those are factors...
Formica? Granite? Composition? Many media to choose from, and the bracing will be determined by the material you want to use in your "table top" LOL!
Are you going to install lighting to shine down on the food? (I would NOT recommend those "pucks" as light source, they get extremely hot!).
What type of wall is this? Brick, Stone? Studs? Drywall? Load bearing wall? Cosmetic wall? All will have a different "need" for shoring up the project.
Decorative trim an mold is up to you, but, dont get too fancy, nor, too plain with it, unless it will match the kitchen and living room on either side.
Ok, my rambling thoughts as they are, and what may come...