Here is a list of milestones appropriate for his age:
Be able to follow simple commands
Says between 5-20 words
Vocabulary made up mostly of nouns
a lot of jargon with emotional content
still should be echolalic... meaning he repeats things he has heard
At this age, his receptive language, what he understands, is more advanced than is expressive language, what he can say. Most of what he says should not be understood by others.
There are common words that children learn like "no" but some children choose to use those words when they are older. Say when they are two years old and you are trying to get out the door to go somewhere...It is a guarantee that they will show you they know it then
He sounds like he is right on track. What you are doing seems to be working as young children learn through imitation. BTW, the milestone chart listed above is for an 18 month old