Welcome to the forums Tim.
Would the new cage be for the new bird or for the current one?
Even if his current cage is getting old or isn't the best I'd wait on replacing it for a bit. A lot will change in his life when all this happens, no need to throw in more change if it can be avoided/delayed.
Starting with an adult you could know her behavior better before you get her, and you could introduce the two before deciding as well.
It may sound like a great idea to get him a friend, but proceed with caution as there are things that could go wrong: they might not like each other, they might like each other too much then not like you.
Also a new bird in the home is just one more change to put on the pile, so perhaps this also could wait until he settles a bit.
Of course if you get him a new cage or friend BEFORE you get him then it would certainly make the adjustments easier.
So, I suppose my thoughts in a nutshell are: try to avoid having too many things change all at once. Birds need routine and consistency.