As the title says, I'm using the default fps template from UE4 (blueprint template) and the movement speed is very high, also I want to adjust the mouse sensitivity, but I don't know where are those values, nor the variables, and my other question is... Where are those values/variables?
The player has a max speed which I've found useful for lowering speed when a player runs out of stamina. To set it up to lower the speed from the beginning, use connect the following to your BeginPlay:
If my memory is correct, the default walking speed is 600 so adjust yours accordingly until the speed is what you want.
With the mouse sensitivity issue, this is just a guess because I've never done it myself but in the Input Settings (Project Settings->Engine->Input) the default scales for InputAxis->Turn are 1.0 and -1.0. I would presume that if you adjust these to lower values, the mouse would move slower.