art assets for prototype

i've been tasked with fulfilling the basic art needs for the prototype of our team pitch "Dungeon Descent" the team suggested a 25x25 pixel box for sprites but i feel like that will be to small for the art style they requested. Jason was very specific that he did not want it to look like and old school final fantasy game which is basically "pixel art" if i up the constraints for size a bit i will have a lot more freedom in building sprites that don't look like the first mario, perhaps a 250x250 box in illustrator that i can scale down to the appropriate size... more on this when i finish a couple of the sprites...