Should I buy from an Apple Store, a reseller, or online? Does it matter where I purchase an Apple product (Macbook Pro), or will I get essentially the same product with the same level of support no matter where I buy it?
If it's a certified apple reseller you will get exactly the same product as when purchasing at www.apple.com or the apple store.

If it's another shop that is not certified by apple, you should ask them (how are we here supposed to know?).

You will get the same level of support. It's worldwide one year limited guarantee with 90 days of telephone support.