4-Carefully cut off the collar, leaving the stand up part of it. If you found a shirt that has a stand up collar anyway you won't need to do this part. Your son can just wear the shirt and pants, or he can add a sash around his hips to blouse up the shirt. He can also wear a plain vest in some solid color like brown, dark green, etc. to be a doublet. The vest material needs to be cotton, wool, linen. or leather to look right.
Sneakers are okay if they are solid black or brown.
Moccasins will look good too. Basically, the less obtrusive the shoes the better. I'll have more details about how I made my daughter's costume up soon. Meanwhile, look at the pics here and on the other sites in the links list for ideas and instructions.