This is an involved topic and needs proper "homework". Learn from an experienced carer. Ring Parks and Wildlife to track down a carer. They can teach you how to feed as well as what to feed. Vet's are also helpful regarding what to feed.

The subject is just too involved so I've given nothing more than a prelimilary guide (see my wildlife index). It's much better to talk to carers repeatedly.

If you feel them and you don't straight away confidently conclude that they are nice and warm, then apply some external heat source and keep it up.

What sort of heat? Heat has it's own dangers, but small, furless animals need a strong source of warmth. Our body warmth isn't enough. Their bedding needs to be almost "too warm" - stifling - uncomfortable to us or a fully furred animal. You are facing the same problem as keeping an lump of meat warm. You have to constantly work at it, especially if they are cold and need warming up. Another danger is that they get cold incredibly quickly - stone cold if you let them. It will happen as you feed them unless you are careful. Feed them while they are still snugly wrapped and still on the heat source.

One radical thing I do to warm a furless animal is to use a warm bath. Once they have warmed up then it's back to the task of keeping them warm. If you slacken off here then they will revert to being a cool lump of meat.

When the animal is fully furred then you can relax. Our body warmth is ideal, but they also can now generate their own heat so it is enough to just leave them snugly in their padded bag. When well grown they don't even need snug padding.

Unfortunately you have to be meticulous about hygiene. No short cuts. You are always having to clean and sterilise everything labouriously and keep equipment isolated from other things to stop bacteria spreading if your sterility does become compromised.

Are you getting put off yet? You should be.

Another value to good hygiene is that it is so much easier to diagnose illnesses. If everything is clean and sterile then there remains much fewer possible causes of the illness, and it is so important to be able to correctly diagnose it. And afterwards, treatment becomes much more reliable.

You should do more than wipe with a dry tissue. You should often wash with a warm wet one first. It may even be easier to just bath them. Don't worry about drying them properly when they are furless. Their skin can't get enough moisture. I put them back to bed while wet. Just make sure they are clean and very warm.

Don't use soap. You don't need to and you also don't need to worry about them licking it up or having some skin irritation.

The principle here is that they were living in a warm pouch with food on tap, and nothing to disturb them. An idillic world. Or, if they are grown, then they'll be used to their bush life, which is peaceful. The more mature they are then the more they will be traumatised psychologically.

A young strong kangaroo almost died from a salmonella infection which developed after a few days of a semitrailer working nearby.

It's all a matter of stress, and that has repercussions directly on health if you are already ill and your life has just been violently turned upside down.

Noises worry animals. They seem to be able to rest through monotonous sounds. It's effects are not so obvious till you drop something and they jump out of their skin. Any banging or clattering must disturb their rest and start wearing them down, even if they don't jump. For newly rescued animals it must be harmful, since it's all part of this alien world they have been suddenly dumped into. Try to give them a chance to temporarily forget that trauma - a bit of brief relief and a badly needed rest.

There is a possible confusion. They love cuddling and gentle petting after they have become used to you. Indeed it may be a psychological need for them. They should be in a pouch which is always moving and their mother should frequently be licking them. I think you should imitate this by carrying them about and petting them. When they get sleepy it may still be beneficial to tuck them into your clothes and carry them about sleeping. You can never know how much each little bit of stress reduction helps them.

If you don't cope well then your caring ability will be eroded.
The times to watch are feeding times. Be prepared. Be ready to deal with an animal that has pood itself. You may have your bottle of milk ready, but what will transpire when you discover a messy, smelly animal whose bag needs changing too?

When you get up for a feed, try to prepare yourself for all the other things you could be confronted with. Get yourself set up with everything at your fingertips.

A valuable preventative measure is routine toiletting after the feed. This trick is also a natural thing that their mother does, and it usually means you don't have to deal with a messy animal. Stimulate pooing and peeing by very gently tickling or stroking the animals bum. Often a warm wet tissue get's them going. Do it over a sink or have some tissues stuffed under their bum as well in the hand that stimulates them and catches the rewards. When the animals grow a bit then the tissues won't cope well at all and I use the sink to catch the urine. Otherwise you could put some newspaper on the floor but this as a bit messy for me.

If you are ready for anything then life becomes a bit of simple work, not chaos.

Periodically test the animal by confronting it with new situations to see what it can cope with. A danger here are foods, but the sooner they are on solid foods then the sooner their development will take off. The danger is diarrhoea . Will a bit of strange food precipitate an upset gut and deterioration of the animal including, to some unknown extent it's future capability to live? Be cautious.

Another important thing when fully furred is exercise. But don't go too far and turn it into another form of stress.

A logical guiding principle is that if they can do something then they are probably ready take on that new situation. Evolution would tend to conspire to make capability and obstacles converge.