Python Network game startup needs expert

Hi
My other questions similar to this have veered off topic or were vague, not specific enough.

My Python RTS server inits a UDP socket and waits for n client HELO messages. It exits the Join Loop and will enter a Game Loop.

My Client first sends a HELO UDP message to the server and will wait for a GAME_START message from the server. (easily done if networking okay)
I'd simply like to know if my outline so far looks okay. I'm most concerned with method and reliability.

I read that one pro network game done in Python had millions of lines of code. Can I get a working game going on my own? What comprises that huge code? I'd guess it's the networking reliability and connectivity? UDP isn't reliable. Is game logic big? Don't some articles mention incorporating TCP for reliability? How is that sewed in exactly, in game, or is it mainly TCP for setup?
My UDP Outline step 0 Code is attached below. Should I do this step all in TCP for safety?

Thanks for comments What should it look like?
Server.py
Client.py