Hello-
My son just turned 4 in February and has outgrown a lot of things that used to concern me about him. For example, just this last year he's finally able to be around loud sounds without becoming terrified or, at the very least, holding his ears. (We'll see how he handles the parades this summer. He loves emergency vehicles but held his ears the entire 4th of July parade last year.) I was always so concerned about this behavior of his but it seemed to just slowly go away on its own. I don't want to downplay your concerns about your son. You certainly know him better than anyone else. If he qualifies for early intervention, and it is successful in helping him, then that is wonderful. However, I don't think the "unusual" fears of a young child are that unusual at all, or cause for great concern. All children vary in how they process sensory information, some are just naturally more sensitive than others. (I think my mother would demand everything to stop if something was in her sock.) Again, you and your doctor are best able to judge if his behavior is within the normal range.. which is quite a large range.
My son still doesn't draw a lot of pictures, either. He prefers to scribble "abstract" works. But he can draw if he wants to, can write some letters... just like your son. So it is mostly a personality thing. This probably isn't so concerning. Your son sounds very bright. The muscle tone concern is something the pediatrician may want to watch, but I don't know what the normal range for gross motor development is.
As far as social fears, my son is very shy as well. He prefers older kids and adults as well. I too have noticed quite a range of how comfortable he is with other kids, depending on the situation and how shy he feels that day, I suppose. We all have different levels of comfort in social situations and some people are naturally more outgoing than others, especially in different social situations. My son takes a while to warm up to other kids, but he will be going to PreK next year, and so I know he will get better at interacting with them. He can be very shy around adults, but he is getting much better at talking to them then he used to be even a couple months ago. So basically.. he is a shy child who is more comfortable talking to older people but he is slowly growing out of it. There is a good chance your child is the same way. I wouldn't worry more than you need to about these things. Kids grow out of most of the behaviors that worry us the most. Researching different disorders on your own will only increase your fearfulness that your child has something wrong. Leave the diagnosis to the professionals and try to relax. With time, patience,and opportunities to interact with other kids, your child will probably grow out of most of these things. And if he doesn't, if a professional diagnoses him with something, then he will get the help he needs and he will still be fine. So don't worry! :-)
Nikki