I plan on hitting up tire rack for a set of tires and shitty rims for the winter. I will have them mounted and balanced. my question is if i get them and bolt them on, do I need to re-alaign the car or am I good to go

Also thinking about downsizing to 17's for winter instead of my stock 18's.

It may not hurt to have it checked when the winter wheels are installed, but in the four years that I've switched wheels/tires on the 6, the alignment has never been tampered with, and at last check, it's still well within specs.

Find a set of used 17" Mazda6 rims. They fit without issues, and they can be found for cheap.

Ooo. Thats a damn good idea about the Mazda 6 wheels. I like where your heads at...Except for that Red Sox Banner being you're from New York...

I plan on putting a set of snow tires on my wife's 06 6i come November. I was kind of disappointed with the limited selection that Tirerack had in this size (215 50 17). I picked up a set of stock alloy rims off of Ebay & will buy a set of snow tires from this website
https://www.tiresavings.com/tireShop.php?action=findCombined
I found that they had the best selection of winter tires for this size. I really do like Tirerack they are very fast & their prices are good, but just to be aware of a couple of things if you do purchase a winter tire/wheel combo from them: 1) There is a good chance that the wheel will come with a plastic sleeve to adapt it to your wheel's size & 2) The offset of the Mazda 6 is different from most aftermarket non-OEM rims, I think the Mazda 6 has a 60mm offset, most aftermarket offsets are about 40mm.