#1. Go to auto-zone, advanced auto, napa, etc. and purchase a $20.00 haynes manual for that specific type of vehicle. In this manual you will find a detailed diagram on how to properly replace your valve cover gaskets. You will need RTV sealant, also purchased at auto-zone, to help seal the VCG onto the valve covers. Also, when you say "plumbing," theonly thing that comes to mind is the plenum gasket on the intake. If you have to remove the intake it's definitely in your best interest to replce it. You do not need to drain the oil out of the crank case unless debris accumulates into the crank case, so make sure you clear dirt, grease , etc. out of the way, keep it clean. As far as leaving your car off for 24 hrs., I would just make sure the engine is cool and then do it. Hope this helps and good luck!
bSt