How the doctor described their biology, I'd think that they would be immune to food like we know food.
Although it takes 5 of them in an orgy to make a baby.
One of the sexes could just full of sedative to dull the carriers immunology so that "she" doesn't excrete the baby during a powerful hickup.
Are there planets in fluidic space, of do they live naturally freestyle in fluidic space?
No planets, where do they get the raw resources and infrastructure to make technology?
They use/have bioships.
Are their ships are a slave life form, beasts of burden with no real sentience, or 8472 mutant/retarded orphans? Or is it like in Aliens where everything is built from the remains of their dead and resin?
Are we sure they are native to Fludic Space?
A million years ago they could have run into Fluidic space to explore or run away from a big bad.
There was no life in the 8 heavily explored galaxies surrounding Skaro according to a throwaway line in Genesis of the Daleks.
It's a mass scaled economy of the only child syndrome.