1. I would use what the kit comes with. if they say itll give u 2/4 then there is more to the kit.
2. I think that shackles take 1" before they drop so a 3" shackle would drop it 2 " I think it has somethin to do with the suspension load or somethin.
3. I have done lowering kits before and the more people u can get the better ur off. buy em dinner or somethin (pizza and beer) worked for me