To get started watch this guys videos:https://www.youtube.com/watch?v=YNAH4C98Qhs
I recommend video goggles like the fatshark ones (or competitors like Aomway) instead of these huge boxey things but they are also more expensive, so that's your decision. Aside from that this is a good starting point. He also has videos on just about anything else if you want to dig deeper.
Also remember that the quadcopter breaks all the time so ideally you want a bunch of spare parts from day 1, nothing sucks more than breaking your first quad after 5 minutes and then having to wait 6 weeks for that replacement part from Shenzhen that is stuck at the customs.
Practising in a simulator is a must. Spend anywhere from 5 to 20 hours in there before attempting to fly a real drone. This will save a whole bunch of crashes. Many people recommend Velocidrone but I personally used the DRL Simulator. It's free and works really well too. They also recruited some people for the real Drone Racing League from there (it has race courses and online timetables). Of course it's a different feeling out on the field with the goggles and you'll realize things like wind exist, but the steering is really similar.
I'll keep you updated about my build, it's nothing too special though.