Welcome!
First, I want to offer an alternative perspective: you didn't squander your abilities. You produced three lovable children, whom you appear to be parenting quite effectively. You became an adult who is able to perceive your child's gifts and needs, and to develop strategies for his success, early enough in his life to increase his opportunities for successful outcomes. You manage all of this while engaging in productive work both inside and outside the home. This is hardly the face of failure, in my book.
As to your child, I think you may have a bit of a better idea of next steps once you have more evaluation data (e.g., the ASD eval) in hand, but much of what you've described seems appropriate. You may also find, if he is indeed on the autism spectrum, that some of the behaviors and characteristics will start to sort themselves out as more closely associated with/originating from giftedness, or from ASD traits, or from stress/anxiety, or from instructional mismatch, etc. As the etiology becomes clearer, the strategies will also become clearer. It takes time to sort out...and then, of course, it changes with his growth and development!
