Maybe this thread will be helpful to you,
It should highlight a specific user that experienced problems with a large project using native PlantPax AOIs.
Most of the PlantPax users that I know don't use the raw PlantPax instructions... they are WAY too bloated. For example, I used PlantPax as a base but then stripped out all of the unnecessary RA garbage and spun the code the way I wanted. I am biased, but I think the code turned out better.
If you are worried about keeping the instructions intact so they are easy to maintain for if/when RA releases updates, then just use them as-is, but if your project is large you will need a beast of a system to keep up.
I don't think you have a warm/fuzzy on how things should really work. I say that because you mentioned the size of P_AIn. Who cares how big it is? You would never copy the entire thing over as you don't need to. Ignition doesn't care, nor need access to a lot of the AOI members.
I recommend that you spend some time planning things. Perhaps looks at the Flintium stuff for inspiration, or just use them as they are. I don't think they ever finished though so you would probably need to finish them.