Basic Functionality -- Code needs to work on Gitlab, code should be tested, you should be using Continuous Integration
A finalized prototype -- The implemention of core functionality should be mostly done by the end of Sprint 3, minus a few bugs or small features. You can still be working on it for Sprint 4, but you want to be sure you can get it deployed by the end of Sprint 4!
Unit tests and code coverage
Adherence to prescribed architecture and design principles
Code reviews (in your Gitlab instance)
Code communication (through Slack/Discord)
Code Metric(s), of your choosing, through a static or dynamic analysis tool (of your choosing). This can be anything except the code coverage tool.
Code Documentation -- Your code should have some basic documentation (can be improved for Sprint 4). In particular, your functions should have some comments, you should have a README at the root of your project that describes how to install/use your project
Other dimensions
Planning activities in Trello board
GitHub use for version control
Slack/Discord workspace use for team communication
