I recently reconfigured my PI planets, so I thought I would share my experiences.
The first time I did PI I did it up near HSC. At the time I did not realize just how bad the hisec planets are compared to nullsec planets. The amount of raw resource you can pull out of the ground is just so much better. Seriously, if you want to do PI "for money" you should move to NSC

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The second time I did PI I did it in the NSC pocket. I made a couple of mistakes this time. Firstly, I didn't consider the tax situation. Taxes on the Customs Stations was high (for nullsec) and I managed to put my planets in 5 different systems, managing to avoid the one system with 0% tax. Doh.
So I recently redid things for the third time (I have a lot of extra isk from moon mining, go moon goo).
This time around, I found the Customs Stations with the lowest taxes. NSC was recently "gifted" several Customs Stations, so that helped.
I knew I wanted to make P2. NSC buyback does not take P1, so I can't sell that and previous researched indicated that P2 was the best to sell on the market.
So I copied the list of P2s into eveprasial.com to see what they were selling for. NSC buyback uses eveprasial.com so I thought it best to base my decisions on what I would actually get for the P2s.
http://www.evepraisal.com/a/y8hxj there's the evepraisal link.
Looking at the "single buy" value, and that'll be what sells the best. Prices vary day to day, so that's the "today price" obviously. The prices are actually quite a bit different from just this morning, sheesh.
It auto-sorts by the "single sell" value, but buyback uses the buy value so ignore the sell value. So pay attention to the buy value.
So you can look at those values, and then look here for how to make things:
https://wiki.eveuniversity.org/Planetary_CommoditiesThe P2 chart on that page will give you the info on to which planets can make which P2. Several types of planets can make P2 without having to import anything from other planets.
For instance, Miniature Electronics have a decent sale price, and you can make those on Lava planets.
Biocells also sell well, and you can make those on Barren planets.
So once you know what sells well, and on what planets you can make those you need to look for the right system. You need customs stations with low taxes, and if you're in hisec you need the Customs Code skill to reduce taxes.
I didn't pay alot of attention to the numbers on the scan bars, I just look for areas on the planets where white areas for the two raw resource are somewhat proximal.
I then place the two extractors as close as possible. Put a Launchpad between them. Route the Raw stuff to the Launchpad.
Then put down four Basic Factories and two Advanced Factories. Route the outputs of everything to the Launchpad.
Route the inputs to the Factories from the Launchpad to the Factories.
Then make sure that the Extractors are producing 12000+ for at least a couple of hours. I also set the time to 3 days.
On nullsec planets that's 2-4 extractor heads.
Some days I Stop/Start the extractors twice a day, sometimes once a day. Whenever I want to. Sometimes I forget. I don't stress about it.