@Terri D.- 1) Yes, you can use your buyers funds from the B to C to close the A to B. I just closed another HUD deal today and I'm going to pick up my check from the attorney tomorrow. Made a profit of $3K after closing costs, which is great and helps me build capital so I can start buying and holding. Also, its very IMPORTANT that you have an attorney that knows what he/she is going because if they mess up, your whole deal is messed up and it will make you look bad. You should start asking attorneys if they can pull off a double close.
2) If you mean how long do you have to close the deal from the day you get the house under contract till it expires, you have 30 days, anything after that you will need an extension and that will cost money. Make sure you get a deposit from the buyer before going under contract because if you go off of the buyer's word and the buyer backs out of the deal, then you WILL lose your earnest money from HUD, I lost my earnest twice because I couldn't find a buyer.
3) No it is not necessary to have the electricity/water/heat/etc on, it's the buyer responsibility to do their own due diligence. Just make sure the information your giving them is correct or else you'll be in trouble. My main cash buyer is a construction worker and all I do is show her the property and she takes over from there. I closed enough deals with her to the point where I dont have to be there all the time, all I do now is drop off the keys and pick them up when she is finished.
4) HUDs arent that hard to close, but since it's your first deal, it's natural to have a lot of questions I was the same way when I did my first one. If you did the right screening and found an investor friendly attorney who can do double closing, you got the deposit from the cash buyer before getting the property under contract, you should be alright. Another tip is that HUD will give you 48 hours to accept the bid or not, I like putting my bids in on Wednesday night so Thursday morning the offer will be accepted and I'll have till Monday to get it under contract, use the weekend to show the cash buyer the property. Best of luck!