Welcome, first of all!
Being on the portly side is not a challenge (to be P.C. I am also "gravitationally challenged"). Despite the popular belief in the US, well fed people are not a bunch of slob idiots! The magic word is FIT. A good tailor can shave 20 pounds of your silhouette, despite the fabric or what else.
Yes, darker colors are better, pinstripe is going to add a good visual effect, but the most important thing is how things are fitting you.
If you are in a...