Yes, the screw WILL show - but just paint the heads with touch-up paint and no one will ever notice.
Bodykit install requires drilling for side skirts and rear bumper - unless you are familiar with drilling through fiberglass/urethane into car body's metal.... I'd recommend leaving it to a professional - you only get one shot and if you screw that up, you cannot just go down to the dealership and ask for another car - you are stuck with that screw-up
Second, a professional is going to know exactly what areas to shave (if required), and will also know how much tightening a bolt needs before it might be too much and cause cracking to the fiberglass (or tearing of the urethane)
As with MOST bodykit pieces, these should be installed by a professional - but I've posted these for anyone who is curious as to how/where the actual install points are located - these photos should answer most of your questions