Yes, you meet the criteria for self employment, with a turnover exceeding £10000.
A Self Assessment tax return is required to declare the self employment income through which you can also pay any class 2 or class 4 National Insurance that may be due on the profits above the threshholds.
The SA1 allows you to register for Self Assessment and National Insurance. You may opt to pay class 2 NIC voluntarily, as it counts towards state pension and benefits. You ca see more information here:
Set up as a sole trader