Hi Happy Mandy, having a greyhound is greyt!! They are affectionately known as 40 mph couch potatoes which is a good indicator as they are either going flat out or are lying upside down on the sofa with their legs in the air. Most are very gentle, sensitive dogs and as others have said are true drama queens. When they come off the track they are excellent on the lead, used to travelling so very good in the car. They are long lived for big dogs - often to 15 or 16 and generally very healthy though they often need their teeth looked at when they come off the track.
Downsides - they are very addictive. Few people stop with one - we now have three. 
Some have what is called a "high prey drive" - this means they will try to chase small furry creatures like squirrels, rabbits and unfortunately things like cats and Yorkshire terriers. Lots of dogs chase cats but greyhounds are fast enough to catch them. I must stress NOT all greyhounds do this - when you adopt from a rescue they will talk to you about this and many will "cat test" dogs before homing and many greys live happily with cats, rabbits etc. You just should be aware of this.
Also, recall is NOT their strong point. When any sighthound sees somethign that attracts their attention they will be deaf to owner and will simply take off, very, very fast. If there is a road in the way they won't even see it - so as an owner, it is your responsibility to make sure you only let them off the lead where it is safe to do so - this is really important and any good charity will go over this with you. Because of this, your greyhound should nver be walked on one of those extendable leads or a narrow collar - they must wear either a martingale collar or a traditional leather greyhound collar, with a proper lead.
Diet - same as any other dog, proportionate to their size. Like any dog, you should worm them regularly. Someone is talking bollocks to you by the sound of it when saying dog food gives worms??? We are in the process of going over to BARF diet, but any good kibble will be fine such as James Wellbeloved. They enjoy bones and these are good for their teeth. Because they are often so tall, make sure your kitchen is tidy - we learned this the hard way!! V talented food thieves!
They hate rain and cold and you should have a coat for them for walking in cold weather - no body fat and a thin natural coat so important to keep them warm. They will take over your sofa and beds - love soft warm comfortable environments.
I would wholeheartedly recommend either South West Sighthounds or Greyhound Rescue West of England - both are very reputable.
Generally when you adopt they will come to you as neutered, vaccinated and chipped and greyhounds also have ear tattoos so you can look up their pedigree and racing history on the database.
Please feel free to ask any questions - I could go on and on and write a mini essay! 