When to register as self employed?

Hello, I was looking for some help please. I am in the process of setting up a small business online making and selling goods from my home. At what stage am I supposed to register as self employed?/ or for self assessment? Do I need to register the name of my business somewhere and if so how/where? I would imagine I will be earning very little to begin with. I'm feeling very confused. I also claim Universal Credit, so have to consider this too, I will have to report my earnings to UC, but does this mean I have to register as self employed even if I earn less than £1000? Thanks

Hi
See guidance at :
Working for yourself
Thankyou.