I have invested a lot of brains and thinking in this project and now I have the (semi-) final concept ready so far.
It consists of a working area with a storage underneath (left part), then the grill with a height adjustable grate and shutters on front an top to simulate a weber grill. Also, with a removable frame for inserting a roasting spit (middle part). Finally, my oil drum smoker contraption (right side) with a separate firebox. Since we found a real ton of bricks unexpectedly, I plan to build everything as brick walls and only pour the countertops from concrete.
The next step will be planning a wood fired outdoor brick or concrete pizza oven.