Clauses using che usually signal the subjunctive (in this case "era ora che"). The verb in this sentence is actually decidersi, which means to make up one's mind. The meaning isn't very different from decidere, so it can be difficult to know when to use which.
In my textbook, it says decidere means to decide, while decidersi means to make up one's mind. To me it seems the two are about the same, but maybe there's just a slight shade of difference in meaning.
Not really correct English. You cannot use "now" to describe something in the past. "It was then that he decided ...." would be the correct way to describe a past event, but of course that does not work here.
"it was the time for him to decide" was my translation. How is that incorrect? It could also be "It was time for decision-making for him" "It was his time to decide". All of these could work, couldn't they?