Where can I find a reference (with carefully written proofs) for basic facts about modular curves? Namely:
Congruence subgroups
The open modular curve $Y_\Gamma$ admits the structure of a Riemann surface (dealing with the issue of orbifold points)
The curve $Y_\Gamma$ admits a completion at the cusps to give a closed Riemann surface $X_\Gamma$
Ideally, with no mention of the word "stack". I'm mostly interested in understanding the complex analytic side of the story.