Personally, I think putting items inside the meat is not required for a good burger. What I would do, is find a good meat vendor that would be willing to do a custom blend of meat. For example, 60% chuck, 20% short ribs, 20% beef brisket. Plus make sure the vendor has taken care of following all the local health regs. As far as seasoning, salt and pepper is all you need. Just need to season right before cooking.
I would go with a 8oz burger, this way you can put a nice crust on the burger and still cook it medium rare and have it stay nice a juicy.
I would seriously not recommend freezing the burger, not as juicy when cooked.
There is a big debate between flat top and char broiler burger cooking method, both have their pluses and minuses. Personally I would use the flat top because the burger cooks in its juices where in a char broiler the juices fall through the grates.
Burger, aged cheddar, and applewood smoked bacon is a basic but awesome combo.
Hope this helps