I dont know how you calculate, but how you are so low (160 DP) ?
I assembled a quick Miasma race, with your ideas in mind, so that the race is still in the trend of what you would like:
Super Scary Miasma Defending Lizards theme :
Prince of Death, Death 9
dominions 8
Hill Fortress
order+3, productivity-3, Heat+2, growth+3, luck-3, magic+3
PoD & death 9, or holy units & death 9 : instill fear into your enemies
hill fortress is an hell to assault (big defence to bring down, then narrow passage & 32 arrows when you assault), coupled with miasma disease, and some city guards should be a good deterrent...
dominions 8 to push Miasma
growth 3 & magic 3 because I had too much design points
. Growth would give you long term power thanks to your population, and +6% income. Magic +3 will make you shamen astonishing researcher, for a low upkeep.
Thats just a quick race, perhaps you can abandon death 9 (but the PoD start at 3, so this is cheap, far less costly that astral or even nature). Also growth 3 is not that needed, you can switch to prod 0.
Dont take the dark citadel anyway, too costly, and no arrows when assaulted.