1. Yes the risk is directly proportiante to the height of the bl. Think of it as a lever.
2. As long as the bumpers(well aftermarket ones) are attached to the frame it's just as strong. The biggest threat is to the steering. I hate the spline type steering extensions.
If you don't jump the rig or drop it off of huge ledges on a regular basis it will hold up fine but be advised that the increased leverage on the sheetmetal and the bodymounts will help accrue metal fatigue. Some of the problems people have had with BL's include cracked cabs. And failed A/C systemns due to overstretched condensor lines.
(Not good in the southern U.S.)
Personally I run a 3" Roger brown BL. I inspect it often and it rides fine.
If I had to get the clearance today I wouldn't do it again however. The bushwacker cut out flares will do you as much good as a 3" bl clearance wise and won't increase leverage at the bodymount points, your center of gravity will be lower and you won't get as tired getting in and out of the truck.
Personally if I am going to keep my truck much longer the Bodylift will be coming off and the Saws all will be put to use. Lower is better.
Of course my Bl will be for sale when all of this happens