A lot has to do with the intended use of a garment, making pockets separate is good if you intend to give the user the option of making them transparent. Modelled details always look better than just painted textures, however there comes a point where you have to consider the polygon count of the model, you have to decide which details are important, I personally usually model the side seams of my garments because they look more realistic like that. As far as positionning buttons, if you have a good modeling programs it's not that hard. What takes the longest IMHO is the uv mapping, that is really tedious if you want to control your textures well.

Dominique Digital Cats Media