if you're working on your own vehicles primarily, invest in the factory service manuals. The haynes and chiltons gives you enough information to make you mad. If you only have a few vehicles, try to find a copy of the factory service manuals on ebay as they can be kind of expensive. Get a lot more reasonable the older your vehicles are.
I buy tools as I need them to do the job. If you try to cover every contingency you'll go broke. If you intend to service your own vehicles it's a good investment. But if you're going brakes, oil changes, belts, etc you don't need a lot of high dollar tools for that sort of thing. I work on my own vehicles and have a lot of different sizes of ratchets, extensions, U joints, a ton of pliers etc because sometimes I think I can work on something without removing everything I probably should and so I have some special tools to gain access. Then sometimes you have to bite the bullet and remove perfectly good working parts to get to what you need.
The first time you do something it does scare you. But once you have a handle on it it becomes easy. then the next time you have the confidence to go a little further. YOUTUBE is your friend. If you have a mental picture of what you need to do then it's not so intimidating to do a water pump, alternator, intake manifold gasket, or other things that people just starting out just look at and scratch their heads and the pros just laugh at us for being so green.
I'm right there with you man, I'm not a pro mechanic either, I'm just good at mechanical things so I can get by doing a lot of my own work. I can say though it's very rewarding when someone quotes you $500-$600 for some work and you do it yourself for the cost of the part. You really feel empowered. having said that, know your limits. I haven't attempted a rear main or timing belt yet. Wasn't there yet last time one needed to be done and I needed the car. But I've grown since then and next timing belt I'm doing myself. Just make sure you have the money for a tow and the money to repair something if you can't fix it or screw it up. if you have that, pound away at it yourself knowing that you have that insurance.