How is a PhD in UK?

How is it doing PhD in UK? I am looking forward for my PhD in UK. My PhD is basically in AI. How is UK for PhD in this topic? Note that, I will have 21000 pound per annum and no tax needed for this. Can I survive perfectly with this money? I am single btw. So no family. And afterwards finishing my PhD, how is the situation of job or starting business and living in UK?