Camber casters plates are definitely a must for the car when it gets lowered that much. Now, onto bumpsteer
The whole idea behind bumpsteer correction is that you have to get tie rod ends working on the same arch as they were when the car was factory height. If you don't, the wheel will steer itself in and out while it's traveling up and down through the suspension motion. Offset bushings accomplish that by moving the rack around, but unfortunately, it's only very little. Bumpsteer kit usually has a LOT of adjustment available at hand, so you can really space out the tie rod end and spindle to get the proper arch back.
Having said that, the cars are still pretty tolerable to drive around with out either of the products, so unless you are fighting the wheel every single time, you don't really need it.