First time raising a cat

You have to take care of its eating, drinking, and even its sex life
When buying, I thought it was the best-looking one in the litter because it was expensive, but I later found out it was a breeding grade
What should I do
Is it necessary to arrange an experienced older sister to introduce it to a more mature diet for the first time
During the introduction period, will it be a problem to let other people’s cats visit(-_・)?