in my opinion, P3 is not he way to go if you want to maximize profit. The P3 market is quite volatile and the market volume in Jita is fairly low which leads to the volatility. P3 is only used by T2 producers in fairly low volumes while P2 is also used in huge volume by people running factory planets around Jita to make P4.
If you can manage the increased volume, a well chosen P2 product will net more. Also it is easier to balance the extraction rates than with P3.
I use extraction planets with two ECUs with 10 heads and a launchpad each to pull maximum rates of P0 (I tend to do a quick export run after roughly 12h to avoid the launchpad overflowing).
I then have factory planets with 7 advanced and 14 basic factories and 1 launchpad and 1 storage unit to produce P2.
My 3 chars and 17 planets take about an hour a day and net 120m+.