Whether you go bilsteins or fox up front a rear coil spacer is pretty common and nothing wrong with it on the rear coils . If you install a spacer larger than 1" on the rear you may want to go with longer shocks in the back . Pretty sure the oem rear shocks are fine with a 3/4 - 1 " spacer .
There are progressive coils avail for the rear , but as stated above I believe they lift the rear about 3" on average and this will require longer shocks .
Really boils down to how much rake you want after lifting the front with the fox or bils .
If you decide to go with spacers on the rear as opposed to coils , make sure you keep the rear coils on there original sides . I've read a few guys getting them mixed up and having to swap them due to one side greater than 1" difference. ( low on drivers side )
Some say they are side spacific due to the the R/S always having the additional weight of the fuel tank , battery and a driver behind the wheel . With a full tank , 200lb driver and battery that's about 400 lbs more on the R/S .
Fwiw , I've had Bilsteins installed at +2.8" for about 14.5 k I have zero complaints and the ride is better than stock imo .
I've heard good things about the Fox as well .
Hope this helps!