"Now everything is fine."
Translation:Jetzt ist alles gut.
They're pretty much interchangable. In past tenses, it's often better to use 'nun', since 'jetzt' always has a more in-this-very-moment-tone. 'Wir gingen nun also nach Hause', that's someone retelling and in that very moment of the past, they started to head home. I don't think you would even use 'now' there in english. We were going home now? Doesn't sound right to me.
I thought about it some more, too. 'Nun' can also be a filling word, like 'well' at the beginning of a sentence. Also, it is less accurate than 'jetzt'. Jetzt is more like right now, nun can be softer, just now, as I described above. We should go now (well within the next minutes) versus we should go right now. The former would probably even be 'Wir sollten nun langsam aufbrechen', we should unhastily start to leave now. Apart from that, not many people use 'nun' in spoken everday speech, it's more often found in written language.
Thanks for the explanation.
No, "We were going home now" doesn't work in English, but if someone was telling a story, it is possible that they would say "Now we were on our way home."
*Edit: I thought about it more and "We were going home now" can work in English in the sense of telling a story. My bad. The use of the present in the past isn't something I come across every day.