'That' is much more natural than 'it' here. I'd also say "to you" instead of "for you", but maybe that's just me. -You wouldn't say "I hope that has been helpful to you" unless you answered their question a while ago and you're saying that hope your response was helpful over a period of time (leading up to the present). -"...had been helpful..." implies that the response isn't helpful anymore and that you hope that your answer was helpful before something happened that made it unhelpful. You could say both "is helpful" and "was helpful". "Was helpful" refers to the time when you gave your answer, and "is helpful" just means in general. By the way, you can say "their" instead of "his/her". If you don't know someone's gender, you can say refer to them as they/them/their.

I hope it has been helpful for you (I hope this answer was helpful and is still helping you now) I hope it was helpful for you (you ask this when you just answered the question because it emphasises the current moment) I hope it is helpful for you (usually.. after you've answered the question, you would hope that the answer already helped the person, or if the person needs the information for a future event, you would say I hope this would be helpful for you/I hope this will be helpful for you, so this is not often used, although used in the form I hope it's helpful for you, which could also refer to 'it was') I hope it had been helpful for you (you can't really use this in this context I think, because an answer does not occur over a period of time, and this past perfect continuous tense is used to refer to events that occur in the past over a period of time that have no definitive ending) so here I offer my answer and I hope that it would be useful/helpful for you, (because you haven't seen this yet and when you do, some time later, I hope it would be[future] helpful for you) :)

Yo creo que las dos primeras son correctas. La primera en presente perfecto y la segunda en pasado para una acción más lejana. Aunque a ver si te respone alguien de habla inglesa mejor!