Add .25-.5 to each shoulder and .75-1" to the chest. I think the collar is fine. Iron the sleeves and let's see them. They probably have the signature Jantzen-first-shirt underarm bagginess, at least it looks that way. Add some to the hips obviously. And if you plan to tuck it in, add 2+" to the length. If not the length is pretty good, maybe add 1". I'd reduce the sleeve circumference a bit as well, at least toward the forearm. Overall, it looks like a shirt that you are just barely growing out of, but not too bad. See how it looks after 10x through the laundry, though. It may shrink considerably.
What changes between the first shirt and subsequent shirts that removes the "first-shirt" bagginess? Also, how do you reduce the sleeve circumference since they don't seem to ask for that detail anywhere? I'm going to be ordering a Jantzen after finding out a little more about proper fit, etc. Things like: where the shoulders on a shirt should properly end, how to have the shirt adjusted so that the sleeves aren't like wings, which particular back pleat looks the best, whether a fly front shirt looks as cool as the diagram, whether a rounded collar with pin hole is acceptible (i want collar bars.), is a white or contrasting collar and french cuff a little much (bought a bunch of nice double enamel links) (maybe even a hidden contrast on both), is edge stitching ok, how to get the two button closure on the collar at the neck that I got on some of the shirts I've bought recently, and how to determine proper "shade of body". I'm also in the process of losing lbs more, so don't want to invest too much in custom shirts yet. But, I don't know if I can wait.