I have a MS6. I have the stocker 18's with summer tires. I was planning on buying 17 inch rims and some winter tires for the winter. Is this the proper bolt pattern. Basically If I get the Mazda 6 17 inch rims (bolt pattern - 5 x 4.50), will it work with no problem?

Yea you can run the Mazda 6 17 inch wheels with no problems at all.
The bolt pattern on all the Mazda's is the same.