Wow, super cool of you to plan something like that for his birthday!
Lots of interesting questions. I've been trying to think up something similar.
One idea I'd consider is just building an island, with all the counter space and storage you'd need. Something that the kettles can go on either side of. I like the look and function of the kettle itself, so I wouldn't want to hide the view (so to speak).
I realize that's not exactly like the vision you were describing, and there are some good examples of guys here who have made some really great looking built in tables, @shoestringshop comes to mind.
Good luck and keep us posted!
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Weber Kettle Club mobile app