To be honest, you don't need to buy any book right now. Use google first. Then, if you need book, then buy one. Cheers!
You can definitely choose on the modules you like as in having a specific online trade of investments manuals or lectures to follow with. Just take your time in selecting before reading it and applying it to your system.
Yes, it is important that we spend our time on the right source, watching different sources is fine but when you enough time to expand your knowledge.