As an author you will be marketing for the rest of your life. It will never end.
As part of the marketing you will join more social media sites than you need or want. You will wonder what to do. You will wonder what will work.
Almost all writers have cats. It's not mandatory but you will be on the outside of the other cat owners. Rare is the author with a dog. Personally, I like birds.
Finishing things are absolutely necessary.
Your friends will not review your book. Your book may not get many reviews. Your book may get zero reviews.