Sorry you had to learn this the hard way!
To address your questions:
1. Regardless of brand, there will always be some that fit better than others.
2. I would always recommend installing yourself if you have the tools and talent. Will save you tons of money in the end.
3. Since I cannot see the scratches you are referring to, I would just say this...if you can feel the scratches with your fingernail, then they will not buff out. If the bumper needs to be painted, it will have to be taken off the car to do so.