The visa in your passport should have been endorsed - that is all.
Re credit. Yes, you have supplied an address for your GC delivery. Use that to apply for the SSN. It may or may not have been applied for, but based on your POE experience, I would bet not. So, in a few days, go to the SSA. It is 2 or 3 hours of glimpsing into another America.
The other thing you can do is try to open a bank account. Some banks will do that without the SSN. You might be bake to get a secured credit card without the SSN, but probably not. However, get the forms and once you have the SSN, open one from abroad with a few hundred bucks and use it on the net for a very small amount. Pay that on time and do that each month. By the time you come back to the USA you will have a credit file.