Is this how it all begins?

It was scary when he was diagnosed with horizontal nystagmus at just 6 weeks old, but we were so relieved to know that he wasn't blind. He continue's to see a pediatric neuro-opthomologist every three months, with the sad understanding that he may one day need surgery.
Pressing forward, we continued to treat Brandt like a normal baby--only, perhaps, a little more spoiled. We spent hours a day laughing, playing, and reading with Brandt.
At four months, I noticed Brandt's muscles were not developing as fast as his cousin (who is just 3 weeks older than Brandt). I tried to shrug it off and tell myself that "every baby develops at his or her own pace."
By six months, however, my worries for him only grew. He wasn't doing much babbling, and hadn't made an consonant sounds. He wasn't rolling over or attempting to crawl. He wasn't sitting up. He had the "rag-doll" effect.
Still, I pressed forward and worked with him every spare minute I had. By seven months, he was rolling over. Just a month later, he was able to sit on his own. It was great to see all of that progress in such a short time!
And, yet, there were still so many other things we wasn't doing--transitioning into the sitting position on his own, pull up to stand, walking while assisted, cruising along furniture, speaking consonants, crawling...
At nine months, I took him to the pediatrician. The pediatrician diagnosed that "rag-doll" disposition as hypotonia, and he referred us for a pediatric therapist for a full evaluations.
Initially, Brandt only qualified for services because of a developmental delay in his speech. He was, however, appointed an ITDS worker who would work with him on both speech and physical therapy. After working with him a few times, she noticed more significant causes of alarm.
She indicated that Brandt's legs "frog" out when he commando crawls and may need a brace to correct. When he is placed in a standing position, he behaves as if he is unaware of how to bare weight. He does not flex his leg muscles, and he wobbles around with "jelly" legs. He does not understand how to move his legs--let alone to alternate them when moving forward.
So, of course, now my mind is plagued with a million questions... What does this all mean? Will he walk? Does he have a delay or a handicap? Where do I go from here? Will doctors perform the tests needed to give me answers, or will they make us wait? Is this the beginning of the rest of my life? Is this how parents of special-needs children find out? What can I do for my son? Or, what did I do to make my son this way???