Nice job on the exhaust. I don't want to be the bad news guy but those hangers won't work that way.
You have the absolute right idea by keeping all the rods parallel so they can slide back forth as the exhaust grows, but those grommets will not stay in place. I know they "snap" together but they are actually designed to work with a through bolt that holds them together.
If you swap out the grommets and the brackets for a different style hanger, like the ones pypes sells or the universal parts store ones you will be fine.