Selling the layout is going to be difficult to anyone that can't stop by your house to pick it up. Besides, layout are personal things and that is usually the one thing a modeler is prone to doing themselves. Packing and shipping a 4 x 8 layout wouldn't be worth the cost and what you would be able to get for it. Best bet, if you really don't want it, donate it to some kids club or a model train group.
As far as your locos, rolling stock and structures, we do have a buy/sell/trade forum here for that purpose. Only thing though, if you do list them on eBay, you cannot post a link here to that sale.
Good luck,