Wow, that would be a Major shame to tear down a layout like that, especially knowing how little you are likely to get, if you really are determined to sell it as a single lot.
My first advice: FIND ANOTHER WAY TO FIND THE MONEY.
If that really isn't an option, if you are close enough to York, and can wait until October, getting some tables would likely give you the best return on your collection. You will probably need nearly until October to dismantle, prep and price everything.
Selling as a single lot will most likely surprise, and disappoint you, on the offers you will likely get, You do have a nice collection, BUT how many people are going to be interested in EVERYTHING in your collection? Out of that number of people who might be interested in EVERYTHING in your collection, seriously, how many are going to be able to afford to offer you more than MAYBE 15% of it's value, all in one lump sum?
It is Sad that you have to sell your collection, but if it must be done, and you hope to put a dent in those wedding bills, you will really need to Man-Up, and put the EFFORT into selling it piece by piece. A large show will give you the best return, in a short time. Price your items to sell, and they will, be unrealistic, or sentimental, and you will be taking them home.
Prices are really down right now, keep that in mind, I recently bought on the bay, a Brand New in the Box, Lionel Tradtional Union Pacific 4-6-2 with TMCC, for $110.00 plus $16.00 shipping, and was the ONLY bidder.
I am Very Sorry to hear of your predicament, and Wish You Much Luck,
Doug