1. Code can usually be reused; some people even use frameworks that already include many of the things you mention. What should be avoided is taking a game you've been working on for a long time and simply using the 7DRL challenge as a "release" for extra exposure.
2. You don't have to post the code or other 'proofs', this is a self-imposed challenge, not a competition. Some people share development logs here or on Discord. The most convenient way to submit a game is to make a WebGL build and post it on itch.io. Once the challenge starts, a "submit your entry" button will appear on the main page, where you'll fill out a form and include a link to your itch.io page.













