I would like to think I am an expert, having always had GSDs 19 over the years, 10 rescues included
The first thing you should be aware of is bringing an eight week old puppy in where a ten month old is,
the older dog will have to be watched very closely as he will not know his own strength and will be
too playfull for the pup unsupervised.

You will have your work cut out training two dogs but it can be done working separately at first until you have control of both together. The pup could pick up bad habits ie. pulling on the lead if Baily does or barking for no reason.

A casterated dog can still become tied when a bitch is in season but obviously there would be no pups,
Not a nice experince if you are not used to it as both dogs could be injured, I would advise to have bitch spayed.
If you decided to have a dog Baily is still young enough to live happily together, but remember you must always be in charge.

Rescue dogs make excellent additions, deserve a forever home and it's not always their fault they are in rescue.

I hope this is helpful.