If you want to make money fast in Elite Dangerous then Exobiology is your ticket. Go for the Stratum Tectonicas on the high metal planets and skip most of the rest. A first footfall collection of Stratum Tectonicas pays 95 million credits. Get out of the bubble 5 or 6K LY and just because a system may already be discovered doesn't mean someone has already made first footfall on a planet.