"Should I find cash buyers first before I make a deal or put the property under contract and then find a cash buyer?"
Some people say you need a long list of buyers before finding deals... At the very least you should know a few buyers and make sure that you're getting deals that those buyers would be interested in.
"How long from when you actually sign the property under contract do you have to close on it?"
You and your seller will set a closing date when you sign the contract. If you close yourself that date can be within days of signing, or if you plan to assign you will most likely set closing date 15-30 days or more to give yourself time to find a buyer.
"Is there any money due up front when getting the property under contract?"
Not necessarily. It's a good idea to put some earnest money down when the contract is signed (deposited with the title company). Some wholesalers give themselves more time in their contract by including verbiage that allows the earnest money to be deposited any time before closing. It's an option but I wouldn't recommend it unless you are fairly confident you can move the property in a very short time frame. It's simply not fair to the seller for you to tie up the property for a month with no compensation if you back out last minute.
The amount of money considered "fair" for earnest money depends on the area, the market, and the seller. Some sellers will get offended if you offer less than $5000 EMD, some are more flexible and open to small amounts. And if the purchase price is only $20,000 a $50 deposit might be enough or you could get away with $10 or even $0.
"Am I able to get out of the contract if the buyer I have lined up backs out of the deal?"
Depends on your contract. Many wholesalers have what's called a "weasel clause". Basically a clause that makes the offer contingent on either getting financing or approval from partner(s) - the "partner" would be your end buyer - which gives you a way to void the offer if you can't move the contract. If you back out you will forfeit your EMD.
"Or what if I never find a buyer to purchase the property?"
This is why you should be in contact with at least a handful of active buyers. Now active is the key word. There are people that claim to be cash buyers and never actually buy anything. If you have, say three buyers that are regularly buying 3 bedroom houses in zip code 12345 and you found a 3 bedroom house in zip code 12345 and were able to get it under contract at a price where the buyer will make their desired profit, you shouldn't have a hard time moving it.
You can network with other wholesalers too. If you are having a hard time finding a buyer yourself, you can either sell the contract to one of those wholesalers (if you have a good enough spread) or share the fee with that wholesaler if they bring a buyer that closes.
"Am I now liable to go through with the purchase myself?"
You don't have to go through with it. That what the contingencies ("weasel clauses") are for. But again you will lose your EMD if you back out.
Or, you could just close on it and give yourself a little more time to find a buyer. Maybe you could even "spruce it up" a bit to add value while you're holding it.