The RTR splitter sits lower than the stock one, and uses those screws, so it may not work...
Just use the factory location... you already have the holes...
I've said it before... get an alignment. These cars all seem to be quite a bit off from the factory... and alignment is covered for 12 months under warranty.
Nothing compares to a large big block with a huge cam normally aspirated... every cylinder firing is a seismic event! My old big block drag car would rattle pictures off of the wall and books off of bookshelves!
As @roket said the +24mm offset works in front, the +50mm offset should be good for the rear, so going that route you won't be able to rotate tires... with a spacer in front you can.
Nice work on the exhaust tips... wish mine were black... I think it looks a bit out of place, as there is not a lick of chrome on the outside of the car (unless you count the stinking badges).
I personally wouldn't go more than 10" in front... I have 9.5 and 11 staggered setup. I think some have used 11 up front, but I believe it requires a spacer to make it work with that offset (I could be wrong)... others that have done it may chime in. @roket did it here...
The PP cars have stiffer springs and thicker swaybars... perhaps try swapping in the base suspension parts for a bit softer ride. Could likely find the parts cheap from someone who is swapping for steeda suspension.
You shouldn't need another alignment, the sleeves will keep it in the same location. I don't have any diff noise... road noise from rear tires is worse though. Their claim of no NVH I think is impossible... you solidly attach a bushing isolated subframe to the chassis... it's no longer isolated!