You need to add the following to your env.local file (and in the environment variables in Vercel/Netlify when deployed).
MY_NOTION_TOKEN=
DATABASE_ID=
You can find more details on how to get these here.
You can update the color palette in tailwind.config.js file.
colors: {
palette: {
light: '',
primary: '',
dark: '',
},
},
Update the manifest.json file and the icons under the public/images/icons folder.
You can use free tools online such as https://realfavicongenerator.net/ to quickly generate all the different icon sizes and favicon.ico file.