You're in the same boat as I was 4 years ago.
I left the IT field for automotive because I enjoy the physical labor more (Some people call me crazy). I was a Cisco Security Analyst and got really bored with sitting at a desk. Mind you I love computer and everything to do with them, but to me its more of a hobby thing in my off time. I never thought of automotive as being something I would do, but I got with this girl and her uncle was kind of a shade tree self proclaimed mechanic. So he started showing me things here and there, whenever he would have a car he was working on he would show me how to do things. After about a year of that, I had collected a massive amount of tools and a massive amount of knowledge.
Starting off, I wouldn't just read manuals or watch videos, you'll never really grasp how to truly do something until you do it. Cars are 100% hands on. A book just won't cut it. Also, tinkering with a junker is kind of small time because not only is it old, but its older just one car, from one year, with one engine. I have worked on over 2000 different vehicles in the past 3 years and none of them are really the same. I could probably tell you how to take a car apart from memory in regards to most GM vehicles. This comes with time though, its very hard for someone like you to get the time to mess around with cars because you're always going to be busy. If you take your time and try to get your own vehicle you can work on that. Thats how I learned. I had a Chevy Malibu and a Toyota Corolla and literally tore them both down and rebuilt the motors just for fun.
You can also make trips to your local junk yard and pull cars apart just to learn about them. I have done this. Not wanting to eff my own car up I would goto the junkyard and just take cars apart and put them back together =P
I think a funny thing that has come from me learning about cars is that I also passively gained alot of confidence with the whole "Do it yourself" thing. I use to be afraid of changing a door knob hahaha Now I'm just like, its broken? Shit we better fix it "Drives to hardware store".
For someone starting out, I wouldn't classify any tools as necessary or not necessary because ALL tools are necessary. You will literally be buying tools for the rest of your life if you're serious about this.
For starters though, I would suggest a socket set (Metric), an extension set, a ratchet, a wrench set (Preferably a large one), pliers, dykes, hammers, 1/2 inch drive sockets and ratchet, and a 3/8" + 1/2" breaker bar(s).
These tools should allow you to work on a vehicle without issue. Unless you doing specialty work you won't need specialty tools.
I hope this is somewhat helpful.
Eric is an incredible mechanic. I've met him personally at one of his seminars, he's very smart and loves doing automotive work. You can learn alot from him, I sure have.