The short answer to your first question is, no. The bumpers, themselves, don't cause as much sagging as would adding a bumper and a winch, but, depending on the spring rate, you may need a leveling kit or you could swap out your current springs with a set of higher rated springs.If you add aftermarket bumpers...
1) Do they always require a lift?
2) how does it affect airbags?
I see various styles. Is it aesthetic or is there something functional to the design here between scorpion/pincer and so on?