Can I keep a German Shepherd and a er spaniel in an apartment?

I live in an apartment which faces the sea and is one step away from the beach. Plus, I work from home, so I can take the dogs out for long walks as many times as necessary. I already have a 4 year old er spaniel, but I love GSDs and would like to have one of them as well. The apartment is on the first floor, and is really big (nearly 2500 sq.ft). It also has a private terrace which is about 500 sq. ft, so space isn't a problem. I just wanted to know if a GSD would be able to adjust in an apartment with another dog.