ARB has been rock solid in my use (own 2 single compressors and one dual setup). A friend had long-term issues with reliability of his Viair compressor. The construction is top notch with ARB and when I've used customer service, I've had no better response.
That's not unusual. Longer, aftermarket springs do that sometimes. I'd make sure it's indexed in the rubber isolators correctly and watch to make sure the spring doesn't rub on anything.
The dealer had mine for 4 hours to do the job. That included checking the alignment and taking it for a test ride. The extra time they quote you is for their convenience, not ours.
U-joints are weaker as the angle is increased. CVs eliminate this factor. So, it should be a safe bet that these factory CVs are stronger than the u-joint axles.
My lower back and legs become very painful on long drives in the JT. I have leather with heat. I spent 7 hours in it a couple weeks ago, using the seat heat on high or medium definitely helped. I find that the JK seats are more comfortable for me.
No, no alignment needed except for centering the steering wheel. I'd be more concerned that they want two days. If I took my time replacing it, I would take a couple hours.