It would be awesome if you rescued/adopted. There are thousands of homeless rats that need homes. A wheel/saucer isn't necessary for rats like they are hamsters. Rats need plenty of outside time where as hamsters can skip a day or two if your busy. You should avoid the ball, rats typically don't like them and it would be a waste of money. They prefer more stimulating toys or just playing with/on you. Most rats are about 10x friendlier than hamsters and they seem to play with you more then on you. But every rat is different. It seems that rats will need to go to the vet at least once through out their life but it may be for something like an abscess. Save up money for emergency vet trips because having rats almost guarantees that you will need to see a vet eventually. You'll know if you have a male, trust me they have huge 'manbits'. The females will...well they won't have them. :P Neutering and spaying is possible though. Neutering lowers chances of fighting between males and it necessary for some males to be able to live with other rats. Spaying lowers the risks of mammary tumours.

In my experience rats make awesome pets. Their personality varies widely but they are just such amazing animals. Be careful they can be addicting though. I started with one, got another one so that the first one wasn't lonely and eventually ended up with 7. :P