Matt your design and craftsmanship are excellent. I like seeing the Kreg jig put to good use, and you hid the pockets nicely on the final product.
My only concern for doing this is the proximity of the cedar to the kettle. If you got the kettle good and hot, I think you could char the cedar or worse, set it ablaze. I have heated my kettle while cooking steaks to the point where I melted the thermoplastic roller/spool on the lid bale. That is likely enough heat to burn something as soft as cedar. I like your idea of using 8 conduit hangers. I think that for safety's sake, there could be more air gap between kettle and cedar and/or some sort of thermal protection, like a BGE gasket or ceramic tiles, around the inside of the ring you cut out. Doing so would mean those conduit hangers would have to be longer, so I would think that means more than 8 would be necessary.
I don't have THE perfect answer. Every mounting idea is somewhat of a compromise. I don't like the idea of drilling through the kettle bottom for a hanging flange the way Performers are factory welded. I have made a table myself, and it is not nearly as good looking as yours. My solution was to hang the kettle from chains that are bolted into the table top. The chains attach at the 3 leg flanges, so they form somewhat of a swing. The kettle is supported by its leg flanges. I have turnbuckles in the chains so that I can have some sort of adjustment on how the kettle hangs. This was my own idea. I should figure out how to post pics of my monstrocity.
I don't think I would do it this way again. Next time I would build a shelf under the kettle and cut down the legs so that they extend only a couple of inches below the ash bucket, and then let the kettle just sit on the shelf. I am 6'4" so any table I build is going to be taller than a standard counter height. This should allow a little storage room under the kettle holding shelf.
I thought I started a thread a couple of years ago about sharing ideas on mounting kettles to tables. I don't know why that didn't catch on.