If you're good and if you're lucky.
If you've never written a novel, those first three books are extremely unlikely to be good enough. You'll have to serve an apprenticeship of a few years just to get your work up to snuff.
After writing for 20 years, having many publications, and having written over a million words, I wrote another novel in 2005, my sixth, I think. Agents rejected it. ("It's good but this genre just doesn't sell" is what a few said, and they couldn't have been more wrong.) When self-publishing came along, I expanded it to a trilogy, published it myself, and it has sold well over 100,000 books. I still make $150/month on it, seventeen years after I wrote it. But I wouldn't if I hadn't kept writing and releasing books. Regular book releases help sell the older books.
Realize, most self-published books make $20-$50 and die a sad death.
So yes, the back list and passive income exists. Think of it as ROA. The book, the intellectual property, is your asset.
Don't just wing it. Be smart about it if you do it. Buy these ebooks at Amazon: Let's Get Digital, Gaughran. The first five books in Chris Fox's Write Faster series. Maybe Dean Wesley Smith's Magical Bakery Book (or go read it on his blog for free), which is about how intellectual property can keep giving through licensing of rights. (as an attorney, he has that view. Fox came from marketing, as I recall.)
Best of luck.