First, take a deep breath. Then realize that he's a young, healthy dog who typically heal broken bones just fine. MOO,
even though it's a weight bearing toe, he still has 3 more hind toes that are healthy. Will he end up compensating and using the other toes more while he's healing? Possibly, but this is what animals do to help the damaged bone heal.
The other questions should really be addressed by your vet. As far as the rain/wetness...put down some towels that
he can walk on from the door to his cage. And keep a towel under him in the cage. The foot should dry out quickly once inside. Have you considered getting him a boot to use temporarily? Then take it off when he comes back inside.
think positively. Injuries happen but injuries heal. Again, he's young and healthy and should be fine once healed.
Look at the questions you’ve posted here, take note and give your vet a call tomorrow and ask them. Even if he/she is busy, a good vet tech should be able to advise you on what to do. I feel so bad for your little guy and you but you will both get through it.
Not a break but my big boy stepped on what I imagine was a piece of glass and it cut clean to the bone in his toe. It completely severed three tendons. As a result his toe sticks out now but it has in NO way held him back physically, and he is a very athletic dog.
Ask your vet for empty saline drip bags, to jerry rig as a temporary waterproof boot, for when he has to go outdoors when it's wet. The plastic is tough. When Nitro was recovering from elbow surgery and on lockdown, we would take him for drives in the car, windows down enough to give his nose a workout. We were very careful getting him in and out of the vehicle.