My almost 5 year old is the same way! He gets easily upset and frustrated! I am having a hard time myself trying to find ways to help him. I just tell him he can do anything if he tries and I just give him love and alot of positive reinforcement! My peditrican feels that it is a maturity thing and he will grow out of it. Some kids take a lot longer to control their feelings. Good luck to you!
How does he feel about it? Does he say he's trying not to cry but he can't help it, or does it not seem to bother him that he's crying a lot?
The truth is, if he cries a lot over small things, other boys will start to make fun of him. Crying over things that really deeply hurt him should not be discouraged - because that cuts off feelings.
But if he's crying over small things, daily, I think you should try to teach him to try not to cry. By taking a deep breath, thinking of something else really quickly, etc.
Best wishes. The fact that he's made a lot of new friends is a really good sign that he's on the right track socially otherwise.