Well, first you should know that Piplup oes evolve twice, so, it needs to evolve for your dex entry. So, if they don't want it to evolve, then that's their problem not yours.
Now, since you sound like you're making this for someone else. then, you just breed the nature and IV stats yourself, then leave the EV training to them. Empoleon is a defensive pokemon, so, you'll probably want decent defense, special attack, and if possible defense and speed as well.
http://www.smogon.com/dp/pokemon/empoleonIf this isn't for anyone else, and it is for you, then, it depends heavily on what your team already has. Empoleon can be ok as a sweeper, but his stats really look like a defensive pokemon. he also has a very wide and diverse set of moves that can be learned. Just, think about your actual team first, then figure out what the best strategy is for making your empoleon fit into your team.
Since you play battle teams you must know all about the fact that just stating one pokemon will make it imposible to figure out an appropriate version.