Do it yourself

I have a double bowl sink with a garburator which now has a dishwasher directly connected to it. They are immediately adjacent to each other. I have to relocate my sink and garburator two cabinets over and around the corner for better use of the kitchen. The drain line will be from the old existing location, so I will have to extend the sink drain about 90 inches (It has to turn around the outside corner of the corner cabinet, so 30" wide cabinet + 24" depth + 36" wide cabinet for a total of 90" of new run. I would like to have my dishwasher drain back into the garburator to maintain the existing drainage configuration, but that means I would have to extend my dishwasher drain (ie the rubber drain line) also 90 inches. Would it be better just to tap into the main sink drain line, which would be immediately adjacent to the dishwasher location, or only a few inches away? Also, I've tried to understand what this "air gap" and looping 30 above the floor is all about but I am still not too sure what it really is for. Is is essentiall venting for the dishwasher drain? Or is is to provide a proper P trap for the dishwasher?