There is an awful lot to learn in this industry. In fact, your post contains topics it would take pages to ,answer: self publishing, traditional publishing, agents, illustration classes, technology. My best advice is to start reading everything you can on this site. Read books. Take classes. Attend conferences. Ramp up your computer skills. Learn how illustration differs from gallery art.
Maybe your local college has computer and/or illustration classes. My son is a professional illustrator. He has a BA in illustration, has worked on textbooks for several years and just had his first book traditionally published. I've learned a lot from him. For instance, a picture of a beautiful room may be art, but if it shows someone's shoe disappearing around the corner of a doorway, it is an illustration, because it tells a story. The story element is essential.
Also be aware that some agents prefer working with author/illustrators. It wouldn't hurt to take a class or two on writing picture books. You can find them online and you can also find books that help tremendously.
It just plain takes time, but you've made a start. You've also recognized you have a lot to learn, so good for you and welcome to the Blue Boards. It's a good place to be.
Laurel