Just a word of warning if you don’t know already, you want to get the 80x80 or 90x90 stencil in combination with the jig and preformed balls for the SoC. A direct heat stencil and solder paste won’t work (or rather your setting yourself up for failure with this type) I’d start with Ram first and go from there.
Details regarding the jig here
don’t know if I covered the stencil to use along with it for the SoC in that topic but it will be there or somewhere else on the forum somewhere 
Under normal circumstances the PMIC is quite resiliant but in cases like this where somebody prior has purposely messed with it it’s hard to say, all depends on what was going on below it after he/she messed with it…
No, search the forum regarding checking your primary rails (resistance relative to ground) which I’ve covered a bunch here to get an idea of if anything is still shorted out and to get a map of the current state of things - if everything checks out then you atleast know what is good if/when you start reballing Ram, PMIC and later SoC (in the event your install goes bad or you damage the chip/s during reflow) all of which you’ll be able to test prior to ever connecteing power (far safer) and/or you find the short and in doing so you’ll be able to determine if pulling the IC’s we’ve discussed resolves the issue (whihc we can narrow down if you do find something) - what you were doing earlier was connecting power up to your SYS rail (which is basically the source voltage for most things and pretty well every other rail derives from it in some way shape or form), subsequent short on 1V8PDR (possibly dragging SYS down as a result) trouble is/was your putting other things in the line of fire doing this.