I am basically in the same situation and all I can do is tell you what has worked for me.
1. Get ZXW Tool! It has pretty much everything you will need including Blackfish with Schematics
2. Use common since first, then try the troubleshooting...meaning if you have touch issues, verify you have a good LCD and Digitizer, Make sure it is plugged in FCP correctly, then try to either reflow/Reball or replace Meson IC)...Grey Bars? Try to reflow/reball or replace Cumulus...No Power? Test for voltages on Battery, then Battery connector on Board that battery connects to. Bad Voltage? Try to replace Tristar, then Tigress, etc...
3. Read, Read, Read as much as you can in Forums and watch as many repair videos as you can on the subject at hand.
4. Get a good Board that has no issues and compare voltages to bad board...Look for Shorts by testing capacitors, they should beep on one side and not on the other...Start with VCC Main row and VCC BAT
5. There are so many things that can go wrong with these phones so try doing searches for the symptoms you are having and find a general consensus on what other techs are doing to repair their similar issues.
6. And finally, do what you are doing now...Ask questions and hope that someone will make an effort to help. Everyone has started out at some point and has been in our shoes and would be happy to help you on your way.
Practice and experience at repairing different problems will get you well on your way...I started with the 6 and 6 plus...then started with the 6s and 6s plus, I will graduate to other models once I get the basics down on these. Write me anytime to bounce ideas around and if I don't have the answer, I will try to help you find it :) Best Wishes and Good Luck!