Some people like to have the endoscopy done even though they know their child has celiac disease based on the blood tests. This gives them a starting point for future healing . . . something to compare future endoscopy results with. That being said, we've been gluten free for three years. He gets regular blood tests and we watch him for symptoms. Since both are normal, I'm not sure we would ever opt for another endoscopy since it is clear he is healing (or healed) Seems like a waste of time and money . . . we don't have to see it to know it is happening.
Like your son, we saw terrible behavior and lots of Autism-like tendencies. Turns out he DOES have Asperger's, (just diagnosed recently) but most of the "obvious" symptoms disappeared when he went gluten free (flapping hands, no eye contact, short attention span, etc.) The terrible behavior was gone in just a few days and he was back to his old, energetic self in weeks. It was like we had a new kid. A miracle really. It never occurred to me that his issues might be caused by what he was eating. We were taken completely by surprise too, but it turned out to be a blessing. Changing his diet was SO MUCH EASIER than dealing with his unpredictable behavior.
If you can get the endoscopy done right away and your doctor requires it for an "official" diagnosis than I would go for it. If you don't need it and waiting for one will delay starting the diet, I would skip it. Depends on your doctor. Those numbers are CRAZY high so it is clear he has celiac.
All first degree relatives need to be tested - even if there are no symptoms at all. I tested positive after my son's diagnosis. What a surprise. I thought my "symptoms" were just me getting old.
If you do have the endoscopy, there is a chance it comes back negative. Don't let that lull you into thinking he does not have celiac disease. The blood tests are clear (and unanimous) . . . the endoscopy does not always find the damage.