I already have RB lower springs and the rear is higher then the front then I like, so what is the simplest and best way to adjust the ride height in the back of the car. How exactly do spring perches work and which ones are best? And if i go the adjustable perch route what springs are needed to be used? Thanks in advance!!

Eibach rear springs with the deadcoils should work just fine.
I cut off 2 deadcoils for my ride height.
***note** Eibach 200# spring on the left, Racing beat spring on the right.
A single coil cut off laying in front, ended up cutting a second coil to get the desired ride height.