If your software already had a working architecture, everything is just plug and play. So estimation is fine. It'll eventually be deliverable. Secondly, admit

If your software already had a working architecture, everything is just plug and play. So estimation is fine. It'll eventually be deliverable. Secondly, admit that all engineering code is tech debt, it'll pay back in future, but don't worry about it. Just be aware you should pay the debt regularly.