Is this the kitchen, or a bar with kitchen functions? Will there be other bar looking things like a foot rail, taps, etc? Or is there a different style? There are all kinds of ways to support granite, including counterweights, corbels and hidden brackets. Do you want a bar ledge, or a wide eating/serving area? Even for an eating overhang, a smaller depth is usually used at bar height than counter height (15" rather than 18"). This is because of the different posture on the different height stools. Remember that the back side of the granite doesn't come finished. If it doesn't require netting to hold the crystals together, you can have your fabricator polish it, but generally one puts plywood underneath more than 6" of overhang, as well as over all cabinets, for stabilization and support. You can hide this with a compound edge.

My best advice would be to discuss the particular size and shape of installation with your fabricator now, while you're designing. He should have the best advice for you.

Also, just so you both know what you're getting, I suggest that you go look at set-ups the same dimension as you're doing, or build it first out of scrap cardboard. The raised bar doesn't really hide much. It creates a firm separation, so that if the cook/bartender is cutting and squeezing lemons right at the lower level counter, the squirts might be stopped by the backsplash, but if you're using standard heights, there's only 6" difference.

Thanks, you are correct the fabricator would be the best resource.

This is not really a kitchen or a bar. Hard to explain but it is a basement kitchenette kind of arrangement. Small sink, under-counter wine cooler, microwave. There will be three or four seats at the "bar". It is mostly just a convenient place to access TV snacks. It is the TV/football room (wife is AVID Steelers fan). It will be used very little other than as a design statement. Used mostly when kids and grandkids visit.

No bar rail.

Given the usage, I think style probably trumps all. I don't know if you'd rather have an eating bar overhang at that point (maybe for grandkid lunches when the game is on?), or if a smaller bar ledge would work best. A final consideration on the height would be the comfort of the sitters. A lot of older people and little kids, as well as short people, have a significantly harder time with bar height stools than counter stools.

As to supporting the bar ledge, and supporting granite in general, you do need good underpinnings. Cabinets need proper braces, and having a few studs to hold up the bar top (to screw brackets into, or whatever) are also a good idea. You didn't say if you were using a designer, or a kitchen specialist at the store, or making your own cabinets. Theoretically, an experienced designer should also know about the supports you'll need, at least in outline.

There are the forums you were asking about, where DIYers share info, perhaps even on GW. A lot of people are on vacation right now, however. I figured someone else would have answered you more knowledgeably about that by now. I opened the thread because I wondered what a "two lever" island was. :) Perhaps you'll get more responses if you repost without the typo. :)