Mounting TV to wall with multiple light switches/outlets
I'd get a stud finder with electrical finder. They come in handy and give a general idea if there is wire running horizontally/vertically.

I'd stay with the longer screws. The horizontal wire from what I've seen is generally ran a foot or 2 off the floor for receptacles so I don't think you'll have to worry about it unless behind the wall is a kitchen and then it runs between upper/lower cabinets. Hopefully the electrician put on nail plates so if you did go where a wire was you'd know it when you can't screw beyond the dry wall.