1. This is a good site with a lot of info and ideas for pet rat owners so check out the different sections
3. Two rats need a cage that is at least 4 cubic feet in size and has a base of at least 30 in by 18 in and height with levels ..... but bigger is better. You will need to replace and wood as it will soon smell pretty bad. Cages also need small bar spacing.
I believe their are animal safe non toxic paints you can use .... because rats and degus will chew on the bars
For bedding you can use unscented paper based bedding, hardwood shavings, at fleece blankets. Dust and odor will cause health issues in rats. Also, bedding needs to be frozen for 72 hours after purchase to kill parasites (mites, lice, fleas etc) that may be in it. Many people use an unscented pelleted paper in their litter boxes such as yesterdays news kitty litter.
2. Rats need to live with at least one other rat, degus need to live with at least one other degu
Rats are predators or prey. They can not be mixed with animals of other species. Rats will kill small animals such as gerbils ..... rats have been known to grab a hamster through cage bars and pull it through the bars dismembering and killing it.
Rats are good pets but they can be expensive. Not only do they need large cages, toys, a solid 12 in diameter wheel, hammocks a house, at least 2 sources of water in the cage - at least one needs to be a water dish
a good quality rat block (oxbow or Harlan Teklad 2014) as 80% of the diet and daily vegs and healthy treats (a piece of fruit, berries, cooked oatmeal, organic pumpkin seeds, etc) Water needs to be free of chlorine and fluoride
but they also need a good vet experienced and knowledgeable in treating rats and they frequently require meds from the vet. Rats become ill and die fast so when you notice they are ill, you are already in a medical emergency. It is suggested that you have a credit card or else a bank account (with at least $300 for the 1st rat and $200 for each additional rat) for medical expenses
Rats need to get out of the cage to run and climb and explore and interact with you at least 1 or 2 hours a day. This is important for many reasons, including allowing you to know your rats well enough that you notice any small change so you can quickly notice if they are ill.
Hope this helps
another good site is joinrats.com
and an important medical site that is vet approved is ratguide.com
Here is a cage calculator to help you decide if a cage has enough cubic feet
http://www.rattycorner.com/odds/calc.shtml