Hikari3747
Basically do you have to write the entire series for a book series then publish it or can you write one book at a time and publish one book at a time?
Self published? You can do whatever you want. Write it all out, then publish, or write it one book at a time. Release it all at once, release it a little bit at the time. With that, you're the boss.
You also won't have many readers. Maybe a few, but not many.
Professionally...In my experiance a book is a six year committment. One year to write, two years to shop it to agents, and three years trying to sell it to publishers. After that I don't think it's reasonable to focus on that project anymore. It might sell, it might not, but if you're working right you should have another book worth working on by the end of three years. So your best bet if you have a series is to outline the whole thing, write the first book, try to sell it and put the rest away. Come up with the next series while you're trying to sell that first book. If the book sells, work on that series. If it doesn't sell, then you'll have another product to shop around while you trunk the first one.