Rule of thumb is about 1-2 Lbs of
LR per G of aquarium capacity. So in your case around 100Lbs. of
LR should be good. Remember that based on the density of the rock you buy, the
LR will take up more of less space in your tank and your water capacity will be reduced (keep that in mind when you need to figure dosing calculations based on water volumes). If you buy the
LR online (it is much cheaper than your
LFS), you can get about 60Lbs. of base rock which is cheaper and then about 40Lbs of
LR that will go on top of the base rock. This will see the base rock until it too is live. If you go this route, you can actually cycle your tank with the
LR in your tank (that's what I did). As far as decorations, the aquascaping is a very personal choice, just make sure that you have good water circulation in the tank with no dead spots. Other than that, decorate to your heart's content. Its your tank and you have to be happy with the way it looks
Most of what you need can be obtained much more affordably on-line. Your
LFS typically will charge around $10/Lb. for the
LR and they may or may not have base rock. Unfortunately you are in a time crunch, but there are some great places that will ship you both base and
LR very quickly.
LR always comes o/nite anyway. Make sure you buy pre-cured only to reduce the chances of unwanted hitchhikers. And also recommended that you pre-treat the
LR to remove any that are still there. Do a search for
LR, hitchhikers and manthis shrimp here and you should get some good information.
HTH. 8)