I liked the UI and spent about 6 minutes adjusting the numbers, you only need to add the night mode and the USDT option with the possibility of merging charts, such as if you invested $100 in Bitcoin and Ethereum, which one is better, and so on. However, I did not find the option to link the crypto API, or is your service to provide advice and notifications, and not real trading through an interface that you provide.

In general, the current site is good and I do not advise you to link the crypto API because you will bear the responsibility of executing user orders correctly. You can give users free coins to use after creating the account and offering features paid in bitcoins.