If I start ATP after already having a PPL, will ATP still provide the opportunity to be a CFII if I pass the rest of the training without busting a checkride?
Zack,
Absolutely. ATP has 2 points of entry, one being with your PPL so you’re fine.
You can even bust a checkride, but I don’t recommend it.
Adam
Yeah, I hear that! Fingers crossed that doesn’t happen!
Zack,
No fingers crossed, practice and prepare… then you can do your best to prevent an unsat checkride from occurring. 
Brady
Good point. I like that idea better. It’s mine to loose.
Zack,
Check out the program timeline on the ATP website. No matter if you start with zero time or PPL you will complete all the ratings through MEI (CFI, CFII and MEI).
As for the checkrides, just focus on one at a time. Prepare accordingly, do your best and the results will come in time…
Hannah