(Dev)Life in the past 12 hours

Oh boy have the last 12 hours been a roller coaster ride for me. Noob me decided to "compile" AoSP for my device to get a taste of how custom ROMs are built from source. Overall it was fun but the errors were a very good excercise for googling, SO. Couple stuff I learnt ( possibly useful for anyone who comes here )
* The shebang line ( #!/usr/bin/env python ) on my system translated to Python 3.7 environment instead of the expected Python 2.7. Best solution I think to avoid confusion is to create a python 2.7 environment and source it.
* Get your trees right. A jar file called WfdCommon.jar ( apparently known as wifi-display common ) was the cause of several hours of hunting the fault. My vendor tree somehow didn't have this file so dex2oat was borking out like mad. I'm still amazed how I figured this one out almost by myself. ( Basically I had to check every file included in the boot class path, and find the odd one )
* I wasted a lot of time in finding the right files to change version numbers and all. Maybe I didn't search XDA properly for a guide ?

Overall it was a fun experience. Also if anyone's experienced in this area could you share resources to learn more about custom ROM development? Specifically on the tweaking part where you mix features from different ROMs to make a great ROM ( like AoSP extended or Pixel Experience ). All I could find were on the zips and not on sources.