Hello DJN87, and WELDCOME to the forum! This is the place to come to if you have questions, and it seems you have a large one. I'll try to help you out here a bit.
First, if you have a rig and tools, then I would guess you could probably head out and try to hire on, undoubtedly as a helper first. Starting out as a helper, even in a shop, is a great way to learn to do it right, as long as you are blessed with a fair teacher to learn from.
Second, you might not want to knock the formal schools; there are many professionals in the teaching side of our industry, and their sole purpose is to teach you what you need to learn. Not to mention, accredited schools usually have pretty decent job placement programs.
You may also want to seriously consider just what you want to do in the industry. It sounds like you're pretty set on pipelining, which is fine, but there are many other options available, such as shipbuilding, general construction, aviation, and fab shops.
In short, how you start out completely depends on what you want to do, and how much effort you throw into it. Good luck!