Anything you put on the bike (rack, panniers, baskets) is going to have be carried up and down stairs, the basket and your backpack sound like your best choice now. I have the Explorer rack you listed, and it's a good sturdy rack. When I use panniers on it, it's harder to maneuver in and out of the condo/office due to the width, and the 3 steps aren't the problem for me that 2 flights of stairs you're dealing with. All things to think about when you're shopping.