That Kicker sub will absolutely fit in the aussie box. I ran one paired with the Kicker Key 500.1 and I was very impressed with it.
FYI - the xmax is 10.5mm. It is not listed on Crutchfield, but if you go to the Kicker website, it is.
https://www.kicker.com/app/tsparam/48CWRT102.html
I can not speak to the Eibachs, but the Bilsteins are going to be a little firmer & you must use your stock springs & upper mount. The Fox kit is a complete swap.
Found this as a quick comparison.
https://www.shocksurplus.com/pages/bilstein-5100-vs-fox-2-0-performance-shocks
They are pre-set to 2" of lift, and are adjustable up to 3".
I installed them as they were in the box & after settling, was right at 2".
This truck was my daily driver & had never seen anything other than a dirt road in it's entire life. The shocks are supposed to go 50K+ miles of street...