Are you looking for an investment property or a residence? You can certainly do cash if you have the ability, however, if you are going to use the property for a residence, I would suggest FHA 203K Rehabilitation loan. It's been my specialty for 21 years and you can literally knock a house down to one wall standing and rebuild (as long as you do not exceed 110% loan to value when it is complete). The home closes "AS-IS", work is completed after closing and it is only 3.5% down on the total purchase price at closing. You can also finance 1-6 payments into the loan if you are doing major structural repairs. The rules are that you have to live in it for 1 year though (2 years is ideal for tax write-offs if you want to flip), but I am unsure of your intention. My website has a lot of information on it if you want to read more about the program http://www.titanhl.com Would be happy to assist you with financing if you choose to go that route!
Once a property is listed, anyone can buy it with cash or financing if all the terms are agreed to. I'm not sure I understand the question, if you have cash to purchase the home of course you can purchase it as soon as it's on the market. You'll need your own agent, as the listing agent represents FannieMae in most situations. Find a great one with lot's of useful experience to get the best outcome.