Started my cycle a week ago- A bunch of little shrimp have appeared?

Do they swim or do they crawl? Swimmers could be Mysid Shrimp.

Some shrimp from the Hippolyte Genus have black stripes but are not common hitchhikers. Same thing goes for Latreutes.

 

They aren't really additions they have been in your tank the entire time, you are just noticing them now. They are not an indication of whether the cycle is done or not. Only way to find out is to test the water.

edit: Also the picture is a amphipod which is what it sounds like you have the way you describe them. I have a ton of them in my tank as well. They are a good part of the cleanup crew and will provide food for some species of fish.