I'm still a beginner, but I learned to build my first gas plane from online resources (many of the people here at this new site helped me at other sites, and at a flight event).
Coming from electric, one of the things I didn't expect was the startle I got the first time I started my plane. After about 20 minutes of starting the plane, not priming the fuel system properly, I thought the plane would never start, and thought I'd just keep going until my arm and shoulder gave out. When the engine finally started, this is what happened. (Fast forward to 7:44)
I think next time I'll get gas to the engine a different way than expecting it to start immediately...