I played Warriors Orochi 2 for the entire summer last year, and played this one for over 140 hours in a few weeks with my friend.
The best thing in this game is to find your 3 favorite characters to use first off,(mine are Nu Wa, and whichever other 2 ppl I want to take out of the other 40 characters that I like using. Usually it is Ayane and Nobunaga.)
Then you should get Agility +10 on your weapons and the item Gauntlets of Vitality.
Depending on how much you enjoy this game and how skilled you are with your team, the difficulty you play on and level of your characters should not matter. :)
Oh, and also, Nu Wa!