-- water parameters required;
I would say that nijsseni can be a little more challenging, especially for breeding. They will prefer a pH well below 6, even for regular maintenance. If you want to avoid bacterial infections and such they will do better with softer, more acidic water. They can be kept in less than ideal conditions, as many fish, but will be less forgiving about maintenance and stress. That said, water is water. It's not really *hard* to make the water soft, it's just an extra step.
-- feeding requirements;
About the same as any other dwarf. If you get captive bred fish you may even get them to take a high quality pellet.
-- aggression levels;
I've found they can be a bit aggressive, but if you are able to get several, let them choose a pair and you shouldn't see too much marital strife.
-- proper breeding set-up;
As Lars said, even a 10 can be used, though I prefer 20 longs in general. More space, room for fry for a while, nice viewing window. But if you've already got the 10, why bother getting another tank. I like planted setups with natural gravel and driftwood, but each their own. Some people use bare bottom tanks and clay pots, so you can choose. Just be sure to use inert materials that won't harden your water and offer them cover for comfort and places to spawn.
-- full adult size attained and recommeded minimum tank size.
Not a real big fish, maybe 2.5" at most for males.
Not to try and steer you away from nijsseni, but have you considered panduro? They are a little easier to breed, similar in color (some would say nicer), and perhaps not so aggressive. I still wouldn't try to keep them in liquid rock though. Try to shoot for 2-3dKH and a pH around 6, and if you can measure TDS, around 100-150ppm.