Yea I would go with what you are thinking. I'm not an expert in this field, but I would be very hesitant to use wood outside. Just my opinion.

 

Why not tile? You could do a natural stone if this is in a weather protected location and you don't mind sealing. Or you could do a porcelain lookalike. Or a porcelain wood look. Or any of about a thousand different looks. I wouldn't do concrete around any cooking surfaces. It's porous and will absorb grease spatters and other food residue.

BTW, your design doesn't look like it uses the minimum recommended aisle space of 3'. 4' would be better. I'm also not really sure what the two different seating areas are for. Wouldn't it be better to have a single seating area done well than two that are "off"? What are your plans for ventilation for your grill since you show this as being in a covered area? And do you envision yourself actually doing a lot of food prep outside, or will all of the food prep occur indoors and then be carried outside? Because there's precious little space between the sink and cooking zone, and that's where all of the major work will take place.