hello， The Nikon-EOS adapter ring fit for nikon AI mount lens and canon EF camera. so the adapter ring fit for your Nikkor 55mm 3.5 ain’t lens on to canon 80d 

yes, the flash can work on Canon 7D 

No the other way this is to be able to mount the Nikon lenses onto the micro 4/3 camera body 

There are 6PCS adapter ring included in this flash, here is the size:
52 55 58 62 67 77mm, as long as your lens size is one of them, then could be used,
Here is the way to check your lens size:
Your camera's lens thread size will be marked somewhere on the lens barrel or printed underneath your lens cap. This number is always preceded by a "?" (diameter) symbol. For example: ?52 = 52mm lens thread size.
If your lens size is none of them, please tell us, we may include the size you need but at this case, this item must be shipped from China so that we could pack with this adapter ring you need. 

I have come to find out that adapter is not compatible with the nikon d5200 and all things would be done manually