Does адрес only refer to house numbers, or can it also mean a speech, like "Gettysburg Address"?
It only refers to house numbers, address as a speech would be "обраще́ние" (although "Gettysburg Address" is "Геттисбергская речь", "речь" is the universal word for "speech").
I believe this is a correct translation and reported it (Sep 12 2018.) To OEp03's comment, "discuss" does not imply a difference of opinion, at least not in American English. I would say it is a very close synonym to "talked about". It is perhaps slightly more formal, but not so formal as to not be used in casual speech.
I'm guessing because Е (like Ю and Я) starts with a Y sound - and об is reserved for real vowels like А, Э, И, У and О
"We have spoken about his address." — not accepted. Should it be? If not, how would one say this in Russian?
Your choice has perfective aspect, so I translate this as "мы поговорили о его адресе".
I forgot to type one d in the word "address" and it was told to be wrong, whereas a similar mistake was noted as a typo. FYI
него is used when it is the object, его when it is modifying the object (same for неё/её and них/их). So, in short, "about him" = "о него" but "about his (something)" = "о его (чём-то)"