Well it can’t be any harder than with Unity 3D, it’s just another language and game engine 
And C++ i’m willing to learn because it is something i need in the future for my dream career, and i’m not ready for a team yet, but i will be at some point because it is required if you want to work in a company.
And how long it takes to make a game, it really depends on how experienced the user are. But you are right, 2 people is better than 1. Everything takes longer no matter what game engine it is, if you are making a game alone, and how much experience the user has with the engine.
But i subscribed, now i’m going to play around with the engine a little, and get going with C++