Guidance for an amateur?

OK, I'll simplify this by having a short, and long version...

Short: I've been playing the bass for over a year, and I'm wondering how to learn all the music theory I possibly can, and I'm wondering what a good place to start would be to improve my skill.

Long (You've been warned): Basically, the only reason I picked up the bass, was because a friend wanted to keep me busy, and he had this vision of starting a band. Yeah, that never came to be, but anyway... I've learned to play in, what I see as, the most non-professional and un-educated way possible. When I decided to finally practice, I just did tabs. System of a Down was my favorite band at the time, so I decided to just learn some of their basslines (like 'Aerials').

It might not sound like much, but I think I've picked up a lot over the year or so I've decided to go head-first into the low-end. I kinda laugh, because I recorded myself playing (that very first time) and then, I play back tunes that I've recently made. When I think I improved, I don't mean figuring out tuning, or how low/high the strap should be, I mean like, my over-all skill.

I've opened myself up to a very VERY broad range of music, just for the sake of developing techniques. I mean, back then I was doing, sheesh, quarter notes on the E string, and getting fret buzz. And now, I'm trying slap/pop and double-tapping (hell no, I don't have Classical Thump memorized yet)

So, I guess what I'm really wondering, is how I can further my skill even yet. I played the trombone for about 6 or so years, so I have a basic understanding of music, but there's a LOT I know that has to be out there. Like what kinda scales there are, for example. I just feel like I'm starting to really take off with this, and I feel like I'm being held back because I just don't know where to go for all the information (Which is why I posted)
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I'm open to any suggestions, and I greatly appreciate any and all of them.

P.S. I got a five string not less than a month ago... and damn, although it took time, I started to like that low B.