If you remember only one thing from all that I've written, remember this: People will notice fit long before they notice whether your suit is fused or half canvassed. Whether the pick stitching on your lapel was done by machine, or by hand. Proper fit - particularly in areas which are difficult and/or expensive to alter significantly - should be your #1 priority.
Extremely good advice, for anyone buying a suit, regardless if it's hus first, or his hundredth. I also agree that there is no substitute for trying them on, physically, in a store, even if you buy in line in the end.