Aren`t you supposed to have perfectly BARE paint, with nothing on it, for PPF install? Meg`s UP has those Trade Secret Oils that can drive me nuts...no IPA isn`t very effective on them IME.
If the surface is already marring-free, then I`d just use some Pre-paint Prep product. If not, I`d correct it to the extent desired and *then* strip whatever might be left on there with, again...the Pre-paint Prep product.
Glad you realized that, and REALLY glad you went ahead and posted it! IMO it speaks volumes as to your having the right mindset.
I wouldn`t rush into the PPF install, figure out everything and then it`s more likely to turn out OK.
OH, BTW...That UPP is what I use on my S8! Looks great and is nice and slick (as long as you reapply it frequently enough) and it`s sure user-friendly, but be warned....IME it provides virtually ZERO protection from etching, so I`d be careful to get any bugs/bird-bombs off it ASAP. I simply LOVE having it on the S8, used it on that one since UPP first came out, but sigh...I`ll eventually replace it because *every* road-trip results in etched paint from either bugs or birds and I can`t keep polishing away such damage or I`ll run out of clear.