it's a bit confusing for me, because in english, "this night would be different," does convey an expectation, but doesn't imply whether or not the outcome matched the expectation. i get that would have been in portuguese requires the participle sido, and not the infinitive, but.. the sense of the two sentences confuses me, in short.
Yes, it is aldo used in Portugal (I can't vouch with certainty if it's more formal and/or common there than here, but it's rather common for regular activities when a habit is formed).
I'm not sure if Whitlam was talking just about the imperfect in that occasion, but "costumar" can also be used in the present for regular activities people keep doing (Eu costumo jogar tênis/ténis no fim de semana. I usually play tennis on the weekend).
What it can't translate is "to be used to" (I was used to having him by my side; I'm not used to hurricanes) which are better translated with the adjectives/past participles "habituado/a" and "acostumado/a" (which follow from costumar, of course; costumar = costume = habit/custom).