Manchester is a very small airport and it will take you 2-3 minutes to get from baggage reclaim then go upstairs and check in again.

Ir you are at Heathrow flying is a good idea. As others have said make sure you get a fare with baggage and maybe go up the night before. You can get reasonable rates for the on airport Hilton hotel.

If you are in central London you can go by train. It will take around 3 hours to get to Heathrow with one change at Manchester Piccadilly.

Congratulations on your forthcoming wedding and have an amazing honeymoon trip to Europe