I believe there is an AA to reduce backstab refresh so that may affect your timing at some point in time.
You really probably won't have any problems using PP in your evade macro (I think a bunch of rogues use it that way). I did this for awhile, but my skillups in PP were super slow doing this so I just dropped it, figuring maybe I'd get an extra swing or two in instead. I ended up working PP on this elf guy (I think he's a wood elf...) that stands outside in the newbie yard of Qeynos right near PoK book. I don't think he could hit me at all even at level 30ish so you can just stand there and pickpocket him all day while he tries to beat on you. Even that took alot of time so I used a bunch of training pts on it to finish it (didn't really have much else to use them on anyhow).