You should also begin preparing for notification that you may be inadmissible under A38 ("excessive demand") as the care of your child will have costs associated with his medical condition. In the end, the visa office will be primarily concerned with the costs involved, but the costs for any special needs child dramatically exceed the excessive demand threshold from what I have seen in the past.
If you have the financial ability to engage the services of an attorney, there are a few that specialize in cases like yours and I can PM that information to you. Fighting CIC on medical inadmissibility is expensive and can cost $5000 or more with the services of an attorney.