Get the cage from Ebay. There are some great buy it now and a lot less than anywhere else. Normally next day delivery from some of the good sellers.
I wouldn't get one too big to start with, they can tend to use one end to sleep and one end to pee if its too big.
Mine were homed by the time they were 3 weeks old (obviously they didn't leave till 8 weeks )
They are such a fab breed to have but be strong from the start, they will jump, bite and have a tendency to headbut when excited!!
When ours got bigger we used a pin down tecnique which basically meant if they get too excited we would hold them down head and bum on the floor and it puts them in a submissive.
Sounds harsh but it isn't and it is exactly what mother dogs would do if pups got out of hand. In fact our elder one often puts her whole body weight on the younger one to pin her down.
You are going to have so much fun
The other thing is with staffies they have such strong neck muscles, collars for lead walking are wasted on them so a harness is better. We got an easy walker which is like a training harness that tightens under their front legs if they pull and it stops the pulling. No amount of tugging on a normal collar and lead will stop a Staffie from pulling!!