I agree that you should hit Off-5th first. But, you should know how a suit should fit you first...maybe they won't have any knowledgeable salesmen at an outlet store like Off-5th.
Some general comments:
If you want versatility, its best to go for a navy blue suit, either solid or pinstripe. If no navy, go for a charcoal gray. While black seems to be very popular, it is not as versatile as these, and would not be a good choice for interviews.
Side vented suit jackets are the most flattering, and are coming back into style.
3 button jackets are best for shorter to average hight, 2 buttons best for tall guys.
Suit should be all wool, or wool and silk or wool and cashmere. No man-made fibres like polyester or nylon.
Off-5th will probably have more higher-end names, like Canali, Corneliani, Valentino, Vestimenta, Hickey-Freeman, and others which should be $500 or less, depends on your luck.
Same for Nordstrom Rack, though they might not have as much higher end stuff.
I'm not too familar with Brooks, but they will only have their suits for sale, which are sack suits generally of a more boxy and conservative cut.
Jos. A. Banks is a decent place for beginner suits. Their signature line and signature gold suits are pretty good. There is almost always a sale going on there, so if you catch them at a sale check out the signature line suits, probably a very good choice for you.
Forget Men's Wearhouse and Macys.