Hi there. Firstly, you are best to get 2 or more rats at a time as they are social creatures and do not do so well on their own. There are situations when they have to be by themselves, like if their cagemate has died or they are too aggressive to be with other rats. But please get 2 or more.
Pets shops like Pets at Home are not a good place to get rats as they use rodent mills to buy their rats from, which are very cruel. See if you can find a good breeder in your area or have a look in a shelter.
Dumbo rats aren't different to other rats apart from their ear placement. They don't live longer/shorter lives (some misinformed pet shops tell people that they do have different life spans).
Don't use sawdust in their cage, use shredded cardboard or clothing/blankets. Get a wire bar cage, not a glass tank. Rats have very sensitive respiratory systems. Also find yourself a vet with good knowledge of rats. It's crazy how many vets there are out there who don't have good knowledge of them.
Feed them a varied diet, this is the best diet they can have: www.shunamiterats.co.uk/shunamite.shtml
A good site for food, bedding, shredded cardboard and toys: www.ratrations.com/
Any more info you need, take a look at this site, it's really good: www.fancyratsforum.co.uk/viewforum.php?f=11 If you register you can have a look at their rehoming section.
Rats need mental stimulation so get toys for them to play with. You will see toys on the Rat Rations site. They also love hammocks. I make mine out of old clothes and blankets. Male rats especially like to just hang out a lot of the time in their hammocks. Female rats tend to be a bit more lively.
Male rats sometimes urinate a little to mark things, so be aware of that. Some do and some don't. Female rats are more prone to mammary tumours which can be expensive to have operated on.
You are best to not spray aerosols in the room your rats will be in. Try to keep them in a room you are mostly likely to be in though such as the livingroom because they love company and are often very nosy.
Any other questions give me a PM because sometimes I forget to come back and check for replies in forums!