Coat: be honest, coats are built to last. So are a lot of undies, but unless you're a beast outdoors (and spend a lot of time in thorny thickets), your coat will definitely last many more years than smalls are supposed to.
This is a Sunday brunch with the guys or family outfit! I feel like you don't have to wear dress pant to wear a blazer with a dress shirt. Just throw on some plain, simple jeans and add on that beige blazer with a neutral color dress shirt.