good luck to you...
Make sure you have all your materials listed....liner (though, I wait until the hole is dug to by my liner, just in case I enlarge as I'm digging), underlayment, pump w/ tubing and couplings, rock, mortar, etc. A pond this large, I suppose you will be digging with some sort of excavator. If you do, don't do too much digging. I find that hand digging the final 10 to 15 percent makes for nice marginal shelves, sump areas, etc. Also, to protect against runoff pollution, be sure that your pond is slightly raised. You might also check into some of the skimmer/biofall set ups that, in my humble opinion, make maintenance easier. Finally, be creative. Don't think too much about where a rock goes...the pond will begin to look contrived. Don't use all the same size rock and try to let the use of rock "bleed" out into some of your yard. If you have access to large rock, use them as stones to sit on and view the pond. Make sure your falls aren't all similar....let them twist and turn and have varying heights.