A big starting island with multiple biomes and boss locations and trader would make a map a lot easier.

Having locations to build that are more secure like islands would also make it easier.

On the opposite end, maps that have a small starting island, and irregular biome spawns can make a map actual hell to play.
I have had plenty of maps with a tiny piece of Plains biome hidden between meadows or blackforest. Allowing of nasty enemies Deathsquito to spawn, while hidden by the trees and hardly visable on the map.

Maps are generated random as mentioned bassed off a seed, so what you get is random. You cant set dificulty options right now, and map generation does not take this into account.
You can however use someone els map seed, by copy/pasting it into the seed text box, when making a new map.