How many is a question that asks for a number ;-) So I am gonna put 10 as an answer.
If you have issues with renpy particularities, maybe you can "hack" them away. It is as simple as putting a text file mystuff.rpy in the game folder (the folder named game) and content like this, to for example add a key binding to auto forward. Some "clever" devs hide the button for it and renpy has no keybinding for it.
init 900 python:
config.keymap['toggle_afm'].append("q")
As for the tools, look at your favorite games in the more information box. Some cite the tools used. For the visual novels, you obviously "need" a visual novel engine. But there are so many, since the tech required for visual novel is so basic. Any engine can display graphics and text and react to user input. Even html. You can code a vn as a website. There is also an engine for that, Twine.
To state the obvious, making a game is an activity that requires multiple tools and areas, that all have their own answer and subanswers. So you need to ask yourself, how do I create graphics? How do I write a (branching) story? Sounds? And so on. And there is tools for all of those.