Secondly, here is a formula for you. Flash index (GN)/ distance from flash to object (D)= aperture value (a). Satisfying this formula, a normal exposure index can be basically obtained with a flash.
Third, the same as above.
As for whether to change the lights, it depends on your needs. After all, Yongnuo 560 does not support automatic metering.
I used Maze's 58AF-2. Nice color temperature