ahh.. the venture into making your own pokemon game.. such a bold decision, though it seems you underestimate the work load involved.. if i were you i'd re-think what you're asking of people, what you have listed is all the things you should be able to do yourself if you want to get into this sort of thing, otherwise it will just be a massive flop when the person you pick get's bored and moves on to other projects. never the less i'm obliged to help, so here: pe2k.com you will find all front, back, overworld, trainer and item sprites there, as for the maps.. you'll probably only be able to get a couple of DS ones, if you want to make a diverse game you'd be better of choosing GBA ones as the style sheets are much more common and easier to obtain. hope this helps man.
-shade