I edited world.dat and used dfhack to get the embark I wanted: an ocean spanning straight across the center of the map, with evil swamps on both shores, and then good forests on either side, all savage. The swamps reanimate. The ocean and swamp share a thralling cloud weather. I haven't found an example of both evil creeping weather and evil rain, so I'm afraid to try modding that in.
Resources are plentiful, but I put 8 layers of sandstone under the soil layers with no ores for those layers, so you have a .. 9? layer aquifer to pierce for most of the map, unless you dig under the ocean, in which case it's only 3 layers of aquifer. Under that is a lot of dolomite, for its high melting point, then a completionist assortment of regular stone layers. For some reason, the caverns are really deep. Not sure why that happened; I haven't parsed out the underground regions yet. I lined up the relative geology depths and terrain elevation so the entire map has homogenous minerals for each layer.
I moved a necromancer tower into the neighborhood.
For normal modding, I used Modest Mod plus giving elves and humans [BABYSNATCHER] so they're always at war with dwarves. Siege thresholds depend only on production, removing population and trade requirements. Also lowered the population and trade thresholds for titans and semimegabeasts to 1 so they can appear any time.
Basically it's a lovely ideal mineral treasure trove underground, but about every bad thing the game is capable of throwing at you is present somewhere on the map. I was trying to pack all the good and bad as possible into one area.