When I got my wheels for snows, steel wheels were not available. Just bought the cheapest alloy wheel. I did not get TPMS for the snows. Discount Tire Direct is the place I got my wheel/tire combo. Free shipping, mount/balance. When you get wheels and tires. Looks like they do have a 17" steel wheel now. Since the smallest wheel for MDX from factory is 18", I would not go smaller. My Tech came with 19" so I got 18". 17" could work fine, but I would not install it. Bolt pattern is 114.3
Here is their website, they have all kinds of offers, rebates, and if you get their Credit card, you get more discounts.
Wheel Products By Vehicle - Discount Tire Direct