Shirt + Jacket question...tailoring?

[TheConstantGardener]

I'm 6 feet, 180 pounds with average build, ...but I have trouble getting shirts and jackets to fit me just right.

SHIRTS: I feel like I'm right between a medium and a large (take JCrew for example). I definitely like slim fit shirts so I usually go with a medium when buying non tailored shirts. But over time my standard sized gut

seems to be stretching the shirts over the buttons down the middle. And my step-dad says they don't fit right on the shoulder because the seem for the sleeve at the shoulder is too "high" or on top of my shoulder.

#1- where should that seem ideally be?
#2- how high up my wrist/arm should a ls shirt retreat when I lift my arms up?
#3- Short of having all my shirts custom made, what is the best way to go when buying shirts then having them tailored to fit right?
.......buy bigger shirts and have the them tailored down?


JACKETS: 40 regular fits me great but I feel like the sleeves end up a bit short when I raise my arms. I guess my question here is similar to my question from above about where the shirt should retreat to when my arms are raised, but please answer that for jackets.

Finally...while I don't believe I can afford to get my future clothes custom made....maybe I could create a better wardrobe by getting a few select items I already have tailored. I definitely can tell the difference and recognize when a man's shirt and jacket fit perfectly (night and day) and wish I could look like that. So any advice, thoughts, links or words of wisdom are greatly appreciated. Ps- I'm currently going through interviews as I on the job hunt which is why I finally got around to posting this question.

Thanks very much!!