He is indeed very young and he probably wants to sleep on you because you are a warm “animal”. Baby buns lie close to each other in the nest, wrapped in the mama’s fur. Your bra is probably an excellent substitute for litter mates. Because he is so young, he should sleep most of the time.
The licking is a grooming behavior and buns display it when they are looking for affection. It has been seen in studies that all mammals enjoy grooming and being groomed, and that grooming increases the levels of oxytocin in the blood. My guess is this is why he grooms both you and himself -it makes him feel safe and calm. It’s not a bad sign. I have an adult bun who is very licky. Rabbits can also groom objects, like pillows or toys.
As for food, I’m sure you’ve read they only eat once or twice per day and fill up really quickly. You should be able to see the tummy get nicely rounded after feeding. They eat so seldom because the milk is extremely rich in fat. Kitten replacement formula is not at all as fat and it’s recommended you mix it with cream.
You can of course weigh him daily to make sure he’s gaining. I weigh my bun in a bowl on digital kitchen scales. Be sure to write down the weight each time -I find it impossible to remember.
I hope you’ll be able to find a wildlife rehabbed who is interested in saving your bun. As Jersey says, it is very difficult.
If he makes it I think he’ll be happy with a plushy toy later on, instead of sleeping in your bra. But for now, your bra really in the best place for him. He should have a plushy (or something like a plushy) and be in a nest box with high enough sides that he can’t wander around when you can’t carry him.