Do I still file a Self Assessment return under Making Tax Digital?

Yes, but it changes shape. At the end of the year you make a final declaration through the software, confirming the figures are correct and complete, by 31 January as before.

The four quarterly updates do not replace it. They feed it. The final declaration is where the rest of your income, your reliefs and your allowances go in, and where the tax is actually worked out.

In the first year you will still file an ordinary Self Assessment return for the tax year before you joined, in the normal way.

The deadline and the process are on gov.uk.