OP
I don't know if you realise this but your cat can become pregnant 48hours after giving birth.
If you choose to let her have the kittens, how are you going to stop her becoming pregnant again before she is spayed?
That's a genuine question. You seem to have made up your mind to keep these kittens but you need to think ahead.
Ask your vet how quickly she can be done after the birth and do not let her out of her house until she is done.
Start saving for vets' bills.
If, and there is no guarantee, it is a straight forward birth you are going to need to get the kittens dewormed, defleed and vaccinated. Ideally you also need to have them spayed before they leave mum.
Cats Protection have been researching early neutering and it can be dine from 2 weeks. Yes that's weeks not months.
Not many vets will do it, but you can start planning now.
I know you have made up your mind, but what you are doing is not in your cat's best interests.