You appear to have quite few items that there are existing markets for and as noted about, over on Model Train Journal there is a group of such folks that appreciate more vintage items, myself included, that would help you identify stuff given parades of pictures.
I can see a good number of cars that I would find attractive as well as that lovely little 4-4-0. There is also a number of circus train modelers about. I think quite a bit may be sellable but w/o seeing each piece up close, that's a bit of speculation.
I think that if you want to liquidate this all quickly, quickly being the operand word, then by all means you contact one of the auction houses that will bundle it up, and sell it off. We'll probably see a good bit of it on eBay a few months later.
If you want to take the time to clean and wipe down everything, maybe get some one local to you involved that knows what these items are and is willing to assist at least in identification, description, and maybe assess functionality of the engines, then you could either take a good portion to one of the major show, e.g. Chicago, and/or parcel it out through eBay where you would reach the largest audience of such vintage items. It seems right now that the prices for such are riding high... Vintage kits are also seeming good prices, so also as noted above, there may be far more stashed underneath waiting for discovery.
As for the layout itself, structures may be salvageable and desirable to some, if not glued down. I'd wager that the rest may be a lost cause, however, there are folks that do want that older & heavier rail, used or not.
